Slide Rule Terms, Glossary and Encyclopedia

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This is a work in progress of words and terms used by slide rule collectors and the relevant history associated of the inventors and manufacturers. When I run across something that I haven't seen before or do not understand, I research it, then add it to this page, as much for my own edification and reference as for yours. Corrections and additions are readily accepted and appreciated. Many topics will have pictures or Links associated with them that you can click.

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3√ scale - Cube and cube roots. (Pickett) See K.

- A gauge mark on Chinese Shanghai Flying Fish slide rules for finding the sinΘ and cosΘ of small angles from 0.573°-5.73°. Located on the C and D scales, rather than Sin and T scales, between 1.74 and 1.75. When the angle is very small, SinΘ is about equal to tanΘ and about equal to the radian of Θ. Set the index of C over the 1° mark on D. For any angle(Θ) on C, read the corresponding sinΘ or tanΘ on D.

4 Inch Slide Rule - These small (literally) group of pocket slide rules are the most compact of all useful slide rules, other than possibly a 5cm (2 inch) diameter circular slide rules. Most have magnifiers on the cursor, like the Hemmi 30, 32 and Aristo 810. The actual length of the scales is 10 cm.

5 Inch Slide Rule - A short, pocket sized,  version of a slide rule with the scales compressed to 12.5 cm (4.92 inch) on a body typically about 15.2cm (6 inches) long in length. Typical precision of a pocket slide rule varies from two to three significant digits, as it becomes difficult to extrapolate between the lines at the right end of the scales. High end examples of pocket slider rules are the K&E 68-1130 (Deci-lon 5), Hemmi 149, and the Faber-Castell 62/83N.

8 Inch Slide Rule - Relatively rare, a shorter version of a standard 10 inch slide rule with the scales compressed to 8 inches, but typically having the same number of tick marks and precision of the longer 10 inch scale. For examples, see Post 1445, K&E 4053-2 and Unique J180.

10 cm Slide Rule - Same as a 4 inch slide rule. 10 cm is the actual starting length upon which the divisions are calculated for a 4 inch slide rule.

10 Inch Slide Rule - a standard length slide rule having the basic scales divided on 25 cm (9.84 inches) with an overall length from 10.5 to 13 inches long. Depending on the construction method, closed or open, simplex or duplex, the body may extend beyond the length of the scales. Standard length slide rules may vary from 25.4 cm (10 inches) to over 30 cm (11.8 inches). The general precision of a standard length slide rule is three (3) significant digits.

12 - A gauge mark on the C or D scale of a commerce or financial slide rule used to denote a dozen, or months.

12.5 cm Slide Rule - Same as a 5 inch or most common standard length slide rule. 12.5 cm  is the actual starting length upon which the divisions are calculated for an 5 inch slide rule.

20 cm Slide Rule - Same as a 8 inch slide rule. 20 cm is the actual starting length upon which the divisions are calculated for an 8 inch slide rule.

20 Inch Slide Rule - An extended length slide rule having the basic scales stretched to twice the standard length of 25 cm (9.84 inches), to 50 cm (19.685 inches) which allows the interpolation of the readings of three (3) significant digits to be more precise. Over time, temperature and humidity, a 20 inch long laminated wood scale is more susceptible to variations in shrinkage and become less accurate than a shorter slide rule as the errors may be magnified because of the length. A slide rule made from an engineering material like aluminum or magnesium, and some plastics, would be proportionally more accurate than one having a wood stock.

25 cm Slide Rule - Same as a 10 inch or most common standard length slide rule. 25 cm  is the actual starting length upon which the divisions are calculated for an 10 inch slide rule.

50 cm Slide Rule - Same as a 20 inch or most common standard length slide rule. 50 cm  is the actual starting length upon which the divisions are calculated for an 20 inch slide rule.

144 - A gauge mark on the C or D scale of a commerce or financial slide rule used to denote 12 dozen, or a gross.

314 gauge point - A mark on the A and B scales and on the C and D scales. It is actually π= 3.14 and is used to find the circumference or perimeter of a circle. Set the index of B under the gauge mark of A, and for any diameter on B, read the circumference on A. See π.

360 hairline - Found on some European multi-lined cursors. Used in conjunction with the central hairline in the center of the cursor. Used as a conversion factor that makes use of the fact that the upper CF scale on the slide and the adjacent DF scale on the stock are displaced relative to the C and D scales by a factor of π or 3.14159. The distance from the "360" hairline to the central line is, in effect 3.6/π or 1.14 (rounded). Positioning the center line over the value of 2 m/s on the D scale read 7.2, the conversion to km/h, on the DF scale.

400g - Centesimal system. Seen next to trig scales on Faber-Castell and Aristo Tachymeter slide rules designed for the surveying market. Rather than the typical circle defined as 360 degrees, these have trig scales defining a circle as 400 grads or 400g.

785 gauge point - A mark on the A and B scales and on some circular slide rules on the C and D scales. It is actually π/4= 0.7854 and is used to find the area of a circle or the volume of a cylinder. Set the index of B under the gauge mark of A, and for any diameter on B, read the area on A. See π/4.




a scale - 1/x, As CI, reciprocal scale.

A scale - x2 - The scale of squares on the body, The square of the D scale.  To determine a square root, find the number on A and read the root on D. The process is reversed to find a square.

Abacus - Calculating instrument that uses beads that slide along a series of wires or rods set in a frame to represent the decimal places. Probably of Babylonian origin, it is the ancestor of the modern digital calculator. Used by merchants in the Middle Ages throughout Europe and the Arabic world, it was gradually replaced by arithmetic based on Hindu-Arabic numerals. Though rarely used in Europe past the 18th century, it is still used in the Middle East, China (Suan Pan), and Japan (Soroban).

Academy - A model series of low cost slide rules manufactured by Blundell (BRL), and later Blundell-Harling (BHL). The "Academy" title was used to denote models of slide rules intended for student use. The first Academy rules were the 300 series, introduced at the same time as the 400 and 600 series Omega rules.The Academy 300 series was process engraved (pressure moulded) using Darvic PVC sheet. Three separate strips were punched along with alignment holes, then machined using a vertical mill. Once fixtured together to maintain alignment, the strips were engraved and filled using filling paste supplied by Croda of Luton. After lining up the components were taped together and end pieces cemented on the reverse side. Finally, the ends parted off by a milling cutter, cleaned and polished. Early end pieces were prefabricated from sheet material but later were injection mouldings. The 300 series were replaced by the 800 series Academy rules. There were even cheaper rules produced than the Academy series. These had S prefixed numbers such as S125 and S143/20 and these were mainly school rules. The later ones S143/10, S143/20, S150/10, S150/20 were open frame, constructed in a similar fashion to the 800 series. The Academy 800 series was an improved version of the 300 series, which introduced new end pieces with extensions that kept the cursor captive. A molded slide lidded box was introduced along with a magnifying cursor. The material remained Darvic. To economize the production, the rules were engraved in sheet form 6 at a time. They were filled all black only.

Accuracy (of a slide rule) - The accuracy of a slide rule is dependant upon the design and construction methodology of the slide rule which determine how well the engraving or printing of all of the scale graduations correspond with the true mathematically-computed positions of every graduation on the rule at the time of manufacture. The measure of the accuracy of the scale is how close a reading or setting is to the true value of the number. The accuracy of a slide rule may diminish over time as the stock warps or shrinks at uneven rates, and as the fit and alignment of the slide and cursor become misaligned. High-end slide rules may offer features that allow the user to adjust the slide rule to enhance the alignment to improve the accuracy. Also Precision (of a slide rule). For an excellent article on the subject, read Slide Rule Accuracy vs. Precision by Alan Morris, Dr.Eng., P.E. (Version 1/29/00).

Acrylic - A transparent plastic used in the construction of post-war slide rule cursors. It is one-half the weight of glass and is easily injection molded in production. Cleaning: Wash with mild soap or detergent, with plenty of lukewarm water, dry with soft cloth or chamois. Grease, oil or tar can be removed with hexane or kerosene. Solvent residue should be removed by washing immediately. Do Not Use window cleaning sprays, scouring compounds, acetone, gasoline, benzene, carbon tetrachloride or lacquer thinner or you may ruin your cursor.

Acu-Math - American brand of slide rule made by Acu-Rule Mfg, first used in 1950. Sterling Plastics continued the use of the brand after purchasing Acu-Rule in 1968, but the name was dropped before 1972 after Borden Chemical bought Sterling around 1970.

Acu-Rule - An American manufacturer of slide rules originally known as Festus Mfg. Co. (1938-39) located in Festus, Missouri. Festus was founded by Paul Jones, jr. became the Acu-Rule Mfg Co. An August 14, 1939 business letter from Acu-Rule Mfg. Co. shows an address of 15 East 26th Street, New York. The company relocated to St. Louis, MO using the brand name of Acu-math. After 1946 the company moved to Mt. Olive, Illinois. "Acu-Design" was tried as a brand name for a brief period, probably to supply slide rules to OEM's like Charvoz-Roos. The Acu-Math Division was later purchased by Sterling Plastics in Mountainside, New Jersey. Early versions began as wood, progressed to magnesium, Like Pickett slide rules, then ended up all plastic. At different times, they supplied OEM slide rules or slide rule components to Dietzgen, Post, Charvoz-Roos, Henschel and possibly K&E. See Dietzgen 1757 Primatrig, Post 1457, Henschel 2020P and Charvoz-Roos SR105D/SR109/SR113. Many of the OEM models had laminated wood (basswood) stocks, while the main Acu-Math line was laminated or painted metal, until all-plastic slide rules became popular. More Acu-Rule History

Addiator - A flat mechanical hand-held 'Troncet Type' mechanical calculator that is used principally for addition and subtraction, sometimes found on the back side of a closed body slide rule. The invention of the addiator is credited to J. Louis Troncet of France in 1889, the first version called the Arithmographe. One of the most popular versions of the Troncet-type calculator was the Addiator, which was created in Germany by Addiator Gesellschaft. Introduced in 1920, over 100,000 units were sold in the first year, and versions of this device remained in production as late as 1982. Featuring a novel carry mechanism, the Addiator could be used to add or subtract, but addition and subtraction required two different control panels. In early versions of these devices, the two panels were provided by flipping an overlay on the front or by having the addition function on the front and the subtraction function on the back (later models had two separate panels on the front). The addiator is comprised of three components, the body containing multiple slides used for calculation, a stylus, and a handle to reset the addiator. The calculations are performed by inserting the tip of the stylus in notches in the metal plates in the addiator. See Pascaline Mechanical Calculator

A.G. Thornton Ltd - See Thornton, A.G., Ltd.

Ahrend - Dutch office supply house founded nn 1896 by 18-year-old Jacobus Ahrend. He first started an office stationery shop at Singel 24 in Amsterdam, under his mother's name: the company was called N.V. Wed. J. Ahrend & Zoon (The Widow J. Ahrend & Son, Ltd). Ahrend soon expanded the range of goods carried to include drawing tables, drawing requisites, collotype machines (a precursor of the photocopier) and water levels. In the 1920s, Ahrend started to sell office furniture and soon saw a rapid increase in the numbers sold. The initial furniture was all made of wood, but it was not long before steel furniture was added to the range. Ahrend celebrated its centenary in 1996, and in that year it was given permission to carry the predicate 'Koninklijk' (Royal). Re-branded slide rules made by Aristo then later Hemmi, were sold and distributed under the Ahrend name.

AI scale - 1/x², Reciprocal of square of D.

Al¹ - Gauge mark equivalent to √(4ρ/π) = 0.1922. Note:ρ=0.029Ωmm²/m at 20°C, ρ is the small Greek letter rho. Used for electrical calculation for aluminum conductors.

Al² - Gauge mark equivalent to √(4/πγ) = 0..680. Note:γ=2.69g/cm³, γ is the small Greek letter gamma. g is the gravitational constant 9.81 meters/sec². Used for electrical calculation for aluminum conductors.

Allen, Elias - (1580-1653) Considered by some to be the father of the slide rule. He was a mathematical instrument maker who worked near St. Clements Church in the Strand in London. He fabricated William Oughtred's first slide rule, advising that it would be easier to make a circular slide rule with opening cursors, rather than the two disk model that Oughtred first designed.

Allied - A U.S. radio and electronics catalog company based that sold U.S. made Pickett and Dietzgen slide rules. It is unknown if any were re-branded.

Alpha or α - Greek letter α

Alro - Dutch brand of circular slide rules.

Aluminum - A non-ferrous light weight metal used by slide rule manufacturers for the body and slide. Alloying of aluminum rapidly developed during World War II which improved the metal to the point that it replaced slide rules previously constructed of magnesium. Reiss and Pickett were large manufacturer's of aluminum slide rules. A thin film of petroleum jelly (Vaseline) is recommended by Pickett to aid in preventing galling ( a problem of aluminum on aluminum contact).

ALRO - A Dutch slide rule company, in the Hague, Holland, that designed and manufactured circular slide rules with characteristic metal boxes.

American Slide Rule Brands - Slide rules manufactured or re-branded by American companies were Keuffel & Esser, Richardson (Geo. Richardson), Gilson, Thacher, Fuller, Pickett or Pickett & Eckel, Dietzgen, Frederick Post, Roos, Charvoz-Roos, Acu-Rule, Acumath, Acu-design, Festus, Lawrence, Engineering Instruments, Charles Bruning, C-thru, Union Instruments, Sterling, Scientific Instruments Co (SIC)(SINCO), Lafayette, Compass, Dieterich-Post, Engineering Sales, Gerber, Guedon, Henschel, Indeco, Jason, Kel-co, Lietz, Novotni, Master Electric, Sans & Streiffe, Micronta, Olson, Omega, Lutz, Slide Rule and Scale Engineering, U.S. Blueprint, Weber, Chirchlow, Mascot, and many others that were promotional rules (list incomplete).

Analon - A revolutionary slide rule by K&E who's introduction was ill-timed with the advent of electronic hand held calculators. The Analon was for dimensional analysis to verify units when doing calculations in physics. Approximately 1000 rules were built in 1967. A large portion of the lot was rejected for quality issues and 597 were known to actually have been delivered to retailers. There were so many returns accompanied with complaints about the difficulty in understanding the manual that the rule was pulled from distribution. The plan was to rewrite the manual was thwarted with the sudden arrival of electronic calculators, makings the Analon semi rare. If you find this white plastic slide rule with gold colored braces in a flea market, take it and run.

Anagit - A proprietary name for PVC plastic used only by the German manufacturer Albert Nestler. It was later replaced by the plastix known as Astrolon as the preferred material for Nestler slide rules.

Antilogarithm - The number corresponding to a given logarithm.

Apollo 11 - NASA's Lunar Lander space vehicle, with the crew Neil Armstrong, Buzz Aldrin and Michael Collins, carried slide rules, for the first time in history, into space and onto the moon, July, 1969. The slide rule of choice was the aluminum pocket Pickett 600-T Dual base Log Log. "We went to the moon with slide rules," retiree Norman Chaffee, who worked on the spacecraft propulsion system, "I didn't even have my first full-function calculator until 1972." Note: When you watch the movie Apollo 13 look for the engineers using slide rules.

Approximate Calculation - A technique, used by experienced engineers and physicists, of rounding your numbers to single significant digits to get a quick approximation of a calculation to verify that your actual result falls in a range that makes sense.

Archimedes - A Brazilian manufacturer of slide rules located in Rio de Janeiro, Brazil (RJ - Brasil).

Aristo - A slide rule manufacturer since 1872, Dennert & Pape was founded by Johann Dennert & Martin Pape, in Hamburg, Germany, and continued under that name until 1936. D&P were the first to laminate and engrave celluloid on boxwood wood slide rules in 1886. Mahogany was used after 1888 and in 1902 started producing slide rules using the System Rietz scales designed by Max Rietz. In 1924 D&P introduced the System Darmstadt slide rule, based on the scales set designed by Prof. Dr. Alwin Walther and began using 'DUPA' as a trademark from 1924 to 1936. All plastic slide rules, using Astrolon for the stock and Plexiglas for the cursor, were introduced in 1936 using the trademark 'Aristo'. D&P officially became Aristo as a company in 1948 when they introduced all-plastic Duplex slide rules and discontinued mahogany wood models. Aristo stayed in the slide rule business until the end of 1978, a run of 106 years. Aristo was one of the most important slide rule manufacturers world wide. Expanded Dennert&Pape/Aristo timeline

Aristopal - A PVC plastic blend used only by the German manufacturer Dennert & Pape beginning in 1936. It is assumed to be the same material as Astralon which appears after 1946.

Arithmographe - French for 'Computing Machine'. Several people experimented with versions of simple mechanical calculators that involved strips of metal with numbers marked on them mounted in a frame, where a stylus was used to slide these strips up and down. A few names that usually rise to the top of the pile in this regard are Claude Perrot (1613 - 1688), who invented an early form of this class of device sometime around the mid 1660s, and the Frenchman Caze, who created his version around 1720. One problem with Caze's machine was that it wasn't possible to perform carries from one column to another. This issue was solved around 1845 by the Prussian-German mathematician Ernst Eduard Kummer (1810-1893). In 1889, a Frenchman named Louis Troncet created his version of this type of calculator, which he called the Arithmographe. Troncet's invention became so popular that the term "Troncet-type" is often used to refer to this class of device, what is now popularly called the Addiator.

Arithmometer - Term used to refer early calculating machines. to an Addiator, which is a mechanical means of addition and subtraction, in actuality, the Arithmometer(s) also were capable of mutliplication and division. Charles Xavier Thomas (1785 -1870) of Colmar, France, or Thomas de Colmar, as he is more commonly known was the first to establish, in 1820, the manufacture of calculating machines as an industry goes to Like Hahn, Thomas used the stepped cylinder invented by Leibniz as his digital-value actuator." Ref:George C. Chase, "History of Mechanical Computing Machinery." Annals of the History of Computing, Vol. 2, No. 3, July 1980. Article: Making the Arithmometer Count

Ash - A type of wood that was commonly used in the construction of Soviet Era slide rules. Fraxinus excelsior (Yasen obiknovenni) and Fraxinus mandschurica (Yasen manjurski - Mongolian Ash) grows in Russia's eastern Siberia and the Ukraine. The wood is very tough and resilient, and is used for farm implements, tool handles, vehicle bodies, baseball bats, tennis rackets, oars, spring boards, piano frames, and to some extent for furniture and interior trim.

Associated Spring Corporation - A U.S. spring manufacturer, based in Bristol, Connecticut, that commissioned specialized slide rules for aiding mechanical engineers in the design of springs. Pickett made some of the earliest versions (copyright 1952) used for designing extension and compression springs and K&E made a slide rule (computer) for designing Belleville spring washers (copyright 1967). There were also cardboard versions copyrighted 1947 through 1960. Today Associated Spring uses computerized software for designing springs.

Astralon - A PVC plastic used by the British manufacturer Blundell Rules Limited (B.R.L.). It replaced Bakelite as the preferred material for slide rules. It was also used by German manufacturers, Faber-Castell (from 1950), Dennert & Pape (after 1946)(Aristo) and Nestler in late model slide rules.

Asymptotic - Mathematical definition: A straight line associated with a curve such that the point moves along an infinite branch of the curve; as in: Vertical Asymptote. Mike's definition: Engineer 'speak' for going vertical or through the roof, what the wife does when she sees more slide rules show up in the mail, or "Becky went asymptotic when she saw the VISA bill."

A.W. Faber - German manufacturer, in Stein near Nurnberg, Germany, named for Anton Wilhelm Faber (1784-1810) who carried on the the work of Kasper Faber's pencil factory (est 1761), followed by son Georg Leonard Faber (1810-1839). Baron Lothar von Faber (4th generation) establishes a factory to build slates, drafting equipment and rulers in Geroldsgrun, Germany and starts making boxwood slide rules in 1882. Celluloid facings were added in 1897. American distributor c1904 in Newark, New Jersey. Name changed to Faber-Castell in 1905 after marriage of Lothar's daughter Ottilie to Count Alexander zu Castell-Rudenhausen. See expanded Faber-Castell timeline.

AZON Corp. - A U.S. manufacturer of drafting media and CAD products, founded in 1949. Mentioned here because in 1987 they acquired Keuffel & Esser Co. in New York, in 1988 acquired Hughes Owens Company in Montreal, Canada, and in 1994 purchased Post & Company in Detroit, MI. These companies were major slide rule manufacturers or distributors that discontinued slide rule sales and distribution in the late 70's. Company is now named InteliCoat Technologies Azon L.L.C.




B scale - x2, The scale of squares on the slide, the square of the C scale.  To determine a square root, find the number on B and read the root on C. The process is reversed to find a square

Bakelite - A non-flammable phenolic resin, invented by Dr. Leo Baekeland, and founder of Bakelite Corp. that was used from 1910 through WWII. Used for early electrical appliances for its insulating and decorative properties. Used in some slide rules like the Novotni Weight Slide Rule for blacksmiths.

Bamboo - The wooden-like material from the Bamboo grass, used by Asian manufacturers of slide rules for the stock, especially out of Japan. See: Sun Hemmi and Relay. The variety of bamboo used in Japanese slide rules (at least by Hemmi) is mosochiku (scientific name: phyllostachys pubescens). Hemmi shipped it in from Kagoshima Prefecture on Kyushu, the southernmost island of the main four islands of Japan. With a fairly large diameter, it was easy to obtain pieces of this variety of bamboo that were large enough to use in slide rules.Ref: William Lise. Bamboo is a light color with light yellow throughout. Easy to precision mill into tongue & groove planks. Over time the colors mellow to a more uniform yellow.

Basic Scales - See Primary Scales.

Basswood - A type of wood used in the construction of U.S. made slide rules with painted or silk-screened scales, from companies such as Lawrence, Engineering Instruments and Acu-Rule. OEM slide rules with Post and Charvoz-Roos brands also may have been constructed with basswood. Basswood grows in the eastern U.S., Great Lakes states, Appalachians and Canada. Related species grow in Mexico. Description: Light, soft, with very fine, even texture, easily worked, good strength for its weight. Experiences high shrinkage when seasoned, but is stable once dry. Color light tan to nearly white. Wood is odorless and tasteless. One of the best carving woods in the world.

Battery - What? Why? History texts will state that the demise of the slide rule was caused by the invention of the electronic calculator, but in some circles it is believed there was a world wide conspiracy of battery manufacturers that sought the end of the non-powered slide rule industry. ...or at least it seems that way (where's my charger?).

Bavaria, Made in - Bavaria is a southern state in modern Germany, Munich being it's most prominent city. In 1806, Nuremberg, the former Free City of the Empire, and large parts of Franconia were incorporated into the newly formed Kingdom of Bavaria. Some A.W.Faber-Castell, Nestler and D&P slide rules are marked with Germany, Made in Germany or Made in Bavaria. The back-stamp was to fulfill the requirements of the McKinley Tariff that was enacted by the U.S. Congress in October 1890 and went into effect in 1891. This law required that all products exported to the United States had to be marked with the country of origin. At first, countries marked their wares with words such as "England," "France," "Germany" and so forth. Sometime after the turn of the 20th century, the U.S. Treasury Department began requiring countries to be more specific in their markings and phrases like "Made in England," and "Made in France" began to appear. The phrase "Made in Bavaria" appeared to be used in the early first quarter of the 20th century, 1900 through WWI (1914-1918), during the realignment of Eastern Europe and the Balkan States, and possibly up to WWII. There was a lot of anti-German sentiment after WWI, so marking products as "Made in Bavaria", helped to continue imports into the US and England.

Bead Arithmetic - Bead Arithmetic is a certain method of reckoning, in which numbers are represented by wooden beads. These beads are systematically arranged on a frame known as the Chinese abacus.The term Bead Arithmetic is used to distinguish it from the other form of arithmetic in which written figures are used. It may be called a science of numbers but, since it is used in daily business life, it is more appropriate to speak of it as an art of reckoning. In its simplicity, it is an advanced method of adding with one's fingers with a memory. Bead Arithmetic, in spite of its usefulness, is not without certain disadvantages. With an unskilled operator it is liable to error because the beads are apt to be moved out of place inadvertently. However, this can be guarded against by carefulness.

Beechwood - A wood used to make slide rules in eastern Europe by Lübker & Company and later Meissner K.G.

Beghin, Auguste - Produced his Règle des Escoles in France in 1907.à This had a displaced scale by √10 and, with the Mannheim rule, became another standard used by a number of manufacturers. He also produced his Règle à Calculs in 1898.

Belcher Brothers - Thomas Belcher began making rules in New York in 1821 and was joined by his brother, William, in 1825. Around 1831, another brother, Charles, joined the firm, and the company's name was changed from T. & W. Belcher to Belcher Brothers. The first rule dates to this period. Around 1843, manufacturing of rules moved to New Jersey and the firm went by the name Belcher & Bros. Around 1853 some of the men's sons joined the firm, and the name was changed to Belcher Bros. & Co. The company had become the largest American manufacturer of rules, but it was surpassed by Stanley in the second half of the 19th century. Belcher stopped manufacturing rules around 1877. References: Otto van Poelje, "Gunter Rules in Navigation," Journal of the Oughtred Society 13, no. 1 (2004): 11-22; Belcher Bros. & Co.'s Price List of Boxwood & Ivory Rules (New York, 1860; reprint, Fitzwilliam, N.H.: Ken Roberts Publishing Co., 1982); Philip A. Cannon II, The Makers and Markers of Gauges, Rules, Squares, and Tapes," .

Berlin, Mayer (Maeir) - An engineer who founded of TECNOSTYL in 1948, a slide rule and technical instrument company in Milano, Italy. Mayer Berlin's sons, Gino and Guido Berlin, still operate the company today.

Bevel - An angular surface that runs along the length of one or both sides of many closed body slide rules. The bevel may contain a linear scale used for measuring metric (centimeters) and/or English (inches), but in some cases may be provide an additional Log scale which read in conjunction, using a line marked on the indicator frame, with the other scales on the face of the slide rule.

Bissaker, Robert - In 1654, Robert Bissaker made the first real slide rule in which the slide worked between parts of a fixed stock. The term, slide rule, applies to all instruments designed so as to allow relative motion between the indices and the scales.

Blundell Rules Limited (B.R.L.) - British manufacturer of slide rules in Luton, England. BRL originated as an effort to create ongoing post-war work for a machine shop created during WW2. The Blundell G1, was their first slide rule (c.1947-1949) which was made of laminated black Bakelite. This highly brittle material was used for two years before switching to Astralon (PVC) as the prior material had a 40% reject rate. BRL later moved to Weymouth in the UK in January of 1956 and refined their rule making techniques, with the British government as a prime customer. The B.R.L. logo was used at this time. In January of 1964, BRL purchased the assets of W.H. Harling Limited of Clapton, London, and with it, a line of precision drawing instruments, T-squares and related items. Harling had previously made wooden slide rules, but dropped them in favor of its other instruments. The resulting company became Blundell-Harling, and stayed in Weymouth which still manufactures specialist drawing equipment.

Body - The non-movable portion , Stock or Stator of the slide rule made of one or more pieces. Bodies were made of wood (Bamboo, Mahogany, Rosewood, Basswood, Magnolia, Pearwood, Boxwood), celluloid laminated wood, sheet metal (steel), aluminum extrusions, machined from stock and molded plastic. Cheap models may have a body made of folded sheet plastic and cardboard.

Boos, Wilfred J. - (1934-1989) Became president of Acu-Rule Mfg Co. in 1946. Lived in Clayton, Missouri circa 1949. Inventor of record of U.S. Patent 2,594,857 which was assigned to Acu-Rule in St. Louis, MO. The patent was filed in 1949 and issued in 1952. An implementation of this patent is the Charvoz-Roos 105D. It is believed that Boos operated Acu-Design for a short time, independant of the Acu-Rule Company, to provide scale artwork to other slide rule manufacturers.

Boykin, Bernard C. - (1921-2011) Designer and manufacturer of the Boykin Rotorule. Born in Ruxton, Maryland in 1921. He earned a BS degree in Chemistry from Williams College in 1942/43 and another BS degree in Chemical Engineering from John Hopkins University in 1954. During World War II he was a radar officer in the United States Navy. Bernard manufactured the Boykin RotaRule from his home in Ruxton, Maryland. His design was started in 1957, with manufacturing commencing in the early 60's. His design was similar to the earlier Dempster RotaRule last produced in 1948, however, the scale order was different and some scales were eliminated, while others were added. Bernard manufactured about 200 total units before the advent of the HP35 forced him to cease production in the early 1970's.

Boxwood - A wood used to make early slide rules, such as by A.W. Faber. After 1897, Faber began to put a celluloid facing on top of a boxwood body. The type of boxwood used for rules was Turkey boxwood, a hard, yellowish wood with an obscure fine grain. This wood was not only durable, but had the essential property of not expanding or contracting with changes in humidity. Thermal expansion is of little consequence in rules, since the normal range of environmental temperatures would cause little change in length. Much more important is humidity, which does vary greatly.

Braces - Also called straps. The end pieces on an Open-Body slide rule that connect the two parallel Stator pieces together. Finer slide rules have braces that are assembled with mechanical fasteners that allow adjustment and calibration of the scales. Braces are typically made of non-ferrous metal or plastic.

Braun, Carl F. - Engineer, Businessman and Founder of the C.F. Braun and Company, an Alhambra based engineering company specializing in the petroleum, chemical and pipeline industry, which had operations worldwide. Carl Braun graduated from Stanford University in 1907. During his under graduate and graduate years, Carl Braun did extensive research and test to develope data to design and predetermine the performance of shell and tube heat exchangers. Over the years, Mr. Braun determined heat transfer rates of various fluids over a wide range of viscosity, temperature differences and exchanger design. As a result of this work, the performance of heat exchangers under widely varying conditions could be accurately predicted. Pickett Industries was contracted to make a Turbulent Flow slide rule (Model 12) after WWII. C.F. Braun and Co. was later owned by Sante Fe International which was bought by Halliburton in 1989. C.F. Braun was also a book collector and devotee of letter press printing and published books as PRIVATE PRESS OF CF BRAUN & CO. In the Art of Stock Picking By Charlie Munger, (Warren Buffett's partner at Berkshire Hathaway) he wrote:" of my favorite stories involves a very great businessman named Carl Braun who created the CF Braun Engineering Company. It designed and built oil refineries which is very hard to do. And Braun would get them to come in on time and not blow up and have efficiencies and so forth. This is a major art.And Braun, being the thorough Teutonic type that he was, had a number of quirks. And one of them was that he took a look at standard accounting and the way it was applied to building oil refineries and he said, "This is asinine."So he threw all of his accountants out and he took his engineers and said, "Now, we'll devise our own system of accounting to handle this process. "And in due time, accounting adopted a lot of Carl Braun's notions."

Braun, Werner von - German rocket scientist responsible for the design of the Nazi V-2 Rocket, and later one of the foremost drivers of NASA space projects. Wernher von Braun brought two 1930s vintage Nestler slide rules with him when he moved to the U.S. after WWII to work on the American space program. Throughout his life he never used any other pocket calculating devices; slide rules obviously served him perfectly well for making quick estimates of rocket design parameters and other figures. (ref: Portrait Slide rule

Breitling Chronomat - A slide rule watch (Chronograph), built from 1940-1978, with a C and D slide rule scale on a rotating bezel. The Breitling Chronomat with its rotating slide-rule was patented in 1941 as war raged through Europe and other parts of the world, its design offering a welcome respite from the plethora of military and military-inspired watches of the period. In 1952, the outstanding usefulness and success of the Chronomat inspired the birth of what has since become the most famous Breitling of all, the Navitimer, a chronograph with the slide-rule redesigned for civil aviation pilots. (Ref: Alan Trott, UK) The Navitar was sent into space with Scott Carpenter in the Mercury program. He asked Breitling if they would make a 24-hour version of the Navitimer pilot's watch, something which would be more appropriate for an astronaut. He was one of the first astronauts to wear a wristwatch in space, wearing his aboard the Aurora 7 spacecraft in 1962. (Ref: Art Simon)

Brevet SGG/SGDG - French slide rule marking. When you read "Brevet SGG" or "Brevet SGDG" on a French item, this means, in French: "Brevet Sans Garantie Du Gouvernement", translated to English: "Patented without government warranty". ie, if the government does not restrict or warrants the product, than the idea is considered original.

British Currency - The former British currency system, found on many European slide rule scales, was based on 12 pennies ("pence") to a shilling (sh) and 20 shillings to a Pound. The entire system was: 2 farthings = 1 halfpenny;  2 halfpennies = 1 penny; 12 pennies = 1 shilling;  5 shillings = 1 crown;  20 shillings = 1 pound;  21 shillings = 1 guinea.  Guineas were used in auctions, specially livestock.  Crowns were not in circulation in the 1900's (collectors items, but valid tender). A 6d piece was a 'tanner', a shilling was a 'bob'. The symbol for the penny (d) was based on the abbreviation of the Latin "denarius", a Roman silver coin (which, confusingly, was initially valued at 10 asses and later at 18). The Pound sign "£" was a handwritten "L", based on the Latin for pound,"libra". When Britain decimalized its money in 1971 it changed to 100 New Pence (p) to the Pound, and retained the same Pound sign. Australia, in 1966, and New Zealand, in 1967, decimalized their former British-based currency systems differently, like several other former British colonies, they completely abandoned the Pound, and adopted a dollar of 100 cents. The Australian and New Zealand dollars were equivalent to half the value of their former Pounds. (reference: Cyril Catt)

British pound (£) scale - Reference to the old British pre-decimal currency. There used to be 20 shillings (sh) to a pound (£), and 12 pence (d) to a shilling. Therefore sh.d scale reads 0 to 20 shilling, and 12 divisions denote pence. These designations, sh.d along with the £ symbol were quite common on European business rules, often in combination with percent, interest or compound interest scales. Because it was not a decimal system, calculations involving parts of a monetary Pound had to be converted to a decimal of a Pound before they could be calculated on a slide rule. Hence the conversions on the log 10 scale.

British Slide Rule Brands - Slide rules manufactured or re-branded by British companies were British Thornton, P.I.C., Unique, Classic, Otis King, Mechanical engineer, Blundell Harling, Boots Ringplan, Jakar, Norton & Gregory, Simplon, Stanley, Technical Standards, W.H. Smith & Son, Fowler, (list incomplete).

Brown, Thomas - (1626 to 1657) (also spelled Browne by some texts) introduced the spiral logarithmic line in 1631, building on William Oughtred's circular slide rule. His son was John Brown (1648 to 1695). One of his slide rules was provided to Samuel Pepys in 1664, which was mentioned in his diary on January 16th, 1664. "Browne of the Minories brought me an instrument made of a spiral line, very pretty for all questions in arithmetic almost, but it must be some use that must make me perfect in it."

Bürgi, Joost - Joost (Jost) Burgi (1552-1632) was a Swiss mathematician and astronomer and is credited with introducing decimal fractions and the application of algebra to geometry. He was a well-known maker of celestial globes, clocks, and other instruments in Kassel. He is also attributed to the invention of logarithms along with John Napier (1550-1617) who gets most of the credit. After reading about an math publication by Michael Stifel that was included in a book by Simon Jacob: Rechenbuch auff den Linien und mit Ziffern (Frankfurt, 1557), Bürgi realised its significance. He designed two rows of numbers representing the essence of logarithms. It is difficult to trace if his ideas were original or second-hand. Yet he is generally cited as the co-inventor of the logarithm. It holds true for both Stifel's and Bürgi's work that neither of their discoveries lead to the design of the slide rule. This was only to come with the activities of Napier.

Business and Finance Rule See also Financial Rule. A special rule (ex: Pickett 510) that has scales that permit one familiar with finance formulas to solve such problems directly, the basic formula being (1 + i)n.

Bygrave, Leonard Charles A British Captain in the Royal Air Force who obtained several patents concerning aids for aerial navigation. Inventor of the Position Line Slide Rule and others. See the article on Position Line Line Slide Rules written by Ronald W.M. Riet in 2008.




C - Gauge mark found on the C and D scales denoting √(4/π) = 1.128 for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.

C' - Gauge mark found on the C scale denoting √(40/π) = 3.568

C scale - x, Principle scale used with D scale to solve multiplication and division problems. To multiply two numbers on a typical slide rule, the user set the left index (start of the scale) on the C scale to line up with one factor on the D scale Division is performed by reversing the multiplication steps by setting the divisor on the C scale opposite the dividend on the D scale and reading the result of the D scale under the C scale index.

C scale (electrical) - Capacitive value in Farads [Pickett N16-ES Electronic slide rule].

C1 scale - Found on some pocket slide rules to give the same precision as a 10" long slide rule. Also D1. Not to be confused with the CI scale.

C2 scale - fx, Shifted scale, functions vary from manufacturers.

C% scale - On a Pickett financial slide rule denoting percent Profit.

Cajori, Florian - (1859-1930) Emigrated to the United States from Switzerland in 1875. Educated at Wisconsin University and John Hopkins and later was Deamn of mathematics at Colorado College. Received his doctorate from Tulane University. He is best known amongst slide rule historians for his book History of the Logarithmic Slide Rule (5.6MB PDF) published in 1909, in which he described 256 designs of slide rules since 1800, 90 of which were produced in the first nine years of the 20th century. Florian Cajori Biography by J J O'Connor and E F Robertson (2000)

Calculigraphe - A watch style circular slide rule manufactured by Henri Chatelaine of Paris, with double-sided bevelled glass. The case was nickel plated. The instrument has two faces, one for numbers, the other (spiral) for sines and tangents. The main key turns the logarithmic scale and the smaller key large pointers on each face. Using the two pointers (one fixed) on the face shown, any interval on the scales (the outer being uniform, the inner logarithmic) may be recorded, and by the subsequent movement of the scales added to any other part of the scales. This was of the Boucher's style design based on the French Patent Breveté, no. 114,520, 13th September 1876. Boucher's patent specification (no. 4310) was taken out in 1876.

Capitol Radio Engineering Institute - CREI - A correspondence school in Washington, D.C. that taught vacuum tube theory from 1927-1954. After WWII, CREI commissioned Pickett to make a slide rule specifically for their students. CREI became CIT in 1955, then in 1984 became Capitol College, still located in Laurel, Maryland. The Pickett N531-ES had the following scales: L, Ln, A [B, CI, C] 2p ,K and LL2, LL1 [S, ST, T, C] D, LL3.

Carbic Ltd - London, England. Manufacturer of the Otis King Patent Calculator from 1921-1972.

Celluloid - The generic name for Cellulose Nitrate, an early plastic made from plant products, that was used to coat or laminate wooden slide rules, first innovated by Dennert & Pape (D&P, later Aristo). Research on Celluloid was begun in the mid 1800's as a replacement for a dwindling supply ivory, and John Wesley Hyatt obtained several patents around 1872, specifically dealing with the manufacturing processes and its use in dental products. In 1886 D&P first introduced white celluloid scales on slide rules and rulers. No maker of slide rules after 1890 ever used ivory, but it is possible prior to 1890. Celluloid compounds were given different names by various manufacturers: Pyralin/Dietzgen, Xlonite/K&E (later Ivorite) and Ivorine/Dennert&Pape (Aristo). From an 1897 Pickworth manual, Instructions for the use of A.W. Faber's Calculating Rule: "The white surface of the celluloid throws the division lines into more distinct relief than is the case with the all-boxwood construction, and in general it is less fatiguing to the eyes. The only objection to the celluloid-faced rule is, that this facing material is somewhat unreliable under variations of atmospheric conditions. However, as the graduations of the Calculating Rule are in every case comparative and not absolute, the expansion and contraction cannot affect the accuracy of the instrument" .Today, highly-flammable celluloid is only used to make billiard balls, having been replaced by other engineered plastics.

CF scale - Folded principle scale where every number on the C scale is multiplied by π. CF= C x π. Note: Scale begins at π (3.14) with 1 in the middle, rather than starting at 1.

CF/π scale - Pickett labeling of a normal CF scale folded at π. Labeled this way to differentiate from their CF/M scale on a model N4.

CF/M scale - Scale unique to Pickett N4 Dual Base Log Log slide rules folded at 1/M=2.30, where the modulus M=log10e. See DF/M. With these scales, logarithms to base 10 may be read from the ordinary C or D scales.

Chained Calculations - Repeated multiplications, where the cursor is used to hold the result of one calculation on D, while the index on C is brought up for the next.

Chan Street - Chan Street of Street Laboratory and Industries of El Segundo, California, designed the Pickett Electronic N-16-ES slide rule, circa 1960, which is labeled as having been "Designed by Chan Street, Los Angeles" (California). This is a specialty slide rule having scales on one side for electronic frequency and impedance calculations to determine tuned circuits. Θ Θ, db, D or Q, XL , Zs or Xc [ C or L, F, λ, ω, T, TR' or X'c, Cr ] Lr, db, CosΘ. The opposite side had a standard Pickett hyperbolic scale set. It is unknown if Chan Street's layout was used on other slide rules. More would like to be known about this individual.

Characteristic - The integral part of the logarithm of a number. See Logarithm and Mantissa.

Charpentier, G. - (c1850) Of France. Designed acircular slide rule is called a "Calculimeter"; "Breveté S.G.D.G."

Charvoz, Andre and Angele R. - Andre Charvoz (1892-July, 1969 died Clifton, New Jersey), Andre Charvoz, born in France, and became president of Manufacture Francais de Compas of Ligny en Barrois, France. Later immigrated to the U.S.A. and was a founder of Charvoz, Inc in 1939 and with his wife Angele, were partners with another family, the Gottheimer's, in the Roos Company which manufactured slide rules in New York. Andre's wife, and business partner was Angele Charvoz (1900-February 1982 died Clifton, New Jersey).

Charvoz-Roos - A U.S. distributor of drafting and engineering supplies based at one time in 50 Colfax Ave, Clifton, New Jersey, that sold Charvoz-Roos branded slide rules. In November, 1939, Charvoz, Inc., formed at 185 Hackensack Street in East Rutherford, NJ. as a joint venture between Andre Charvoz, president of Manufacture Francais de Compas of Ligney-en-Barre, France, and Samuel Sanders of Teaneck, N.J., president of L. Oppleman, Inc. The Roos Company of 280 Madison Ave., New York, was a partnership between Andre and Angele Charvoz, and Abel and Ethel R. Gottheimer, that was created (c1941) to manufacture painted wood and laminated wood slide rules in the United States presumably to replace foreign imports of slide rules during WWII. It is possible that parts of the Charvoz-Roos early slide rules were supplied by the U.S. slide rule manufacturer Acu-Rule as many parts are identical with other brands of the time. Roos began distributing Charvoz drafting supplies by 1945. After the war, Roos Company merged with Charvoz Inc. into Charvoz-Roos Corporation on June 14, 1946 and began importing re-branded Relay/Ricoh slide rules from "Occupied Japan". The manufacturing plant in East Rutherford, New Jersey was sold in 1953 and the Charvoz-Roos Manufacturing Company was in receivership. Around 1954 the company became just Charvoz, and slide rules were imported from the German company Aristo. Early Roos and Charvoz-Roos slide rules were identical to Post 1442, 1447-D, 1452-D, 1462 and Henschel 2020. A Charvoz-Roos PSR-200 is identical to a Relay 403 and an Aristo 909 is branded with just 'Charvoz'.

Chemical Milling - See Photoetching

Chemist's Rule - Most major manufacturers made a version of a slide rule with specific scales to aid in the mixing of chemical compounds, to solve reacting-weight equations (K&E 4160, Post 1490, Hemmi 157).

Chinese Slide Rule Brands - Slide rules manufactured or re-branded by Chinese companies were China Sha, China Shanghai, Ding Feng, Flying Fish, Haiou Pai, Hangzhou, Jang, Paper, Ruyi, Shanghai, Sida, Xuesha, and Tianjin Squirrel (list incomplete).

Chisel Cursor - (or Metallic Runner) A one piece metal, typically brass, cursor used prior to 1900 and as late as 1905, to assist in the transposition of reading the values on simple slide rules, typically with only the A[B,C]D scale set. Either the left or right side was used to align the divisions on the scales. The chisel cursor was replaced by glass cursors with central hairlines mounted on celluloid spacers or metal frames.

Chronograph Watch - A watch with a C and D slide rule scale on a rotating bezel. The Mimo-Loga, a non-chronograph, was introduced during 1941. The Mimo-Loga, including a later version sold under the Girard-Perregaux brand-name, is virtually unknown today. The Swiss made Breitling Chronomat with its rotating slide-rule was patented in 1941 and was sold through 1978.

CI scale - 1/x, This scale is the reciprocal of C scale.

CIF scale  - Folded scale of the reciprocal of C. See CF scale.

Circular Slide Rule - A slide rule bent around in a circle. The cursor is a pair of radial arms that move around the origin. The advantage of the circular slide rule is that you can fit a longer scale, and many more tick marks, within a certain area. Circular slide rules and rules with spiral scales were made before 1733, but their inventors are unknown. One model is still being manufactured today by Concise in Japan. From a 1988 speech by Seymour Cray (1925-1996), father of the super-computer, In college I had a circular slide rule, the 10-inch model. That's as big as circular slide rules were made, so I had the very top of the line. If you had a circular slide rule, you had some social problems in college. Almost everyone else had a straight-stick slide rule, and they came in a nice leather case with loops on the back so you could hang them on your belt. Those of us with circular slide rules couldn't do that, so people looked at you kind of funny and thought, `Do you suppose he's really not an engineer?'.

Cleaning Slide Rules - DANGER, DANGER, Will Robinson! Many collectors have destroyed a perfectly good artifact in an attempt to clean their slide rules of the ravages of time. The ISRM curator predominately limits its cleaning of specimens using Antiseptic grade Isopropyl Alcohol and a soft cloth. This is good for removing common dirt and grease from handling and for the red or blue ink from drawing pens when the slide rule was used as a straight edge. Alternately, Eric Marcotte in Canada has provided a number of experiments and methods for the Care and Cleaning of Slide Rules and cases and provides much good and cautionary advice on restoration.

Cleveland Institute of Electronics - CIE - Founded in 1934, CIE was a home-study electronics school and after WWII, commissioned Pickett to make a slide rule specifically for their students. CIE still operates out of Cleveland, Ohio. The Pickett N515-ES had the following scales: (LG), (fx)2p, A [(Cr)B, S, T, (Lxor Cx)CI, Xlor Fr-C] D(XL), L, Ln.

Closed-Body Slide Rule - A slide rule having a body fashioned out of one or more pieces that has a bridge between the upper and lower halves, common to earlier designs. The channel formed by the bridge sometimes contains additional scales or tables. See Open-Body Slide Rule.

Code Maker - A specialty type of slide rule, popular with kids, that was made by Lawrence Engineering right after WWII for making secret messages by reassigning the values of the alphabet. The slide rule could be used for coding and decoding messages, as long as the user knew what 'key' was assigned by the original writer. The pocket version was the Dick Tracy Secret Code Maker named after the famous cartoon detective.

Coggeshall, Henry - (1623-1690) Suffolk, England, an expert in mensuration and timber gauging. In 1677, he combined the proportional circle with a slide rule, thus developing the 'polymeter', the earliest standard slide rule design. This instrument was a a standard linear design, but in 1682, he used the basis to establish the carpenter's two-fold, two-foot rule, which incorporated a 'sliding Gunter' in one leg of the rule for performing timber calculations.

Coggeshall Rule - Made by Stanley Rule and Level Co., New Britain, Connecticut, 32x4x.4 cm. Wood and Brass hinged on two sides. Had Navigational scales including meridian, chords, latitudes, and hours inscribed.

Compass - American brand of slide rule manufactured by Relay/Ricoh out of Japan. The Compass 1321 was the same as a Relay 150 and the Compass 505 is the same as a Relay 505. Known date codes span 1956 through 1961.

Computer - Up to 1960, "computer" was understood to be a person who computed usually with a slide rule close at hand.. A computer who must make many difficult calculations. Now dictionaries begin the only definition of "computer" with "An electronic machine..." From the preface of a 1953 Pickett Trig Slide Rule manual :"A computer who must make many difficult calculations usually has a book of tables of the elementary mathematical functions, or a slide rule, close at hand."

Competition, Slide Rule Competitions were and are still held to challenge mathematical problem solving using slide rules. Japanese students in Tokyo competed as early as 1952. US Schools in the 40's had student contests in "Slide Rule and Number Sense". Up until 1980, a national US competition was held in Texas by the University Interscholastic League (UIL) an extension of The University of Texas founded in 1909. The Pickett 905-ES Texas Speed Rule was designed for this competition. Cole's manuals (like Cliff Notes) were available to prepare for district, regional, and state slide rule competition in the UIL. The UIL still holds competitions but the slide rule contest was phased out for the calculator. Results from 1945-1980 Since 2001, there is an on-going World Championship Slide Rule Competition in Texas, promoted mostly by slide rule collectors. The 2006 championship was held on March 4th in Irving, TX.

Concise - A Japanese company that still makes slide rules of the circular variety. They provided re-branded, promotional and custom products to Pickett, Scientific Instruments, Lafayette, Fullerton, Sama & Etani and others. Company Link

Concrete Quantity Calculator - A slide rule with scales to calculate the volume in cubic yards or meters of concrete required to fill a 3-dimensional space. Typical scales are Thickness(A), Width or Height(B), Length(C) and Volume(D). Designed by George L. Lockhart in 1940 and originally produced by Slide Rule & scale Engineering Co.

Condition of Slide Rule The condition of a slide rule may be described with the slide rule condition rating system of the Dutch Circle of Slide Rule Collectors, endorsed and used by The Oughtred Society :
    C0 Mint condition, with all extras such as box, case, instruction
        manual present also in mint condition, factory clean.
    C1 Mint condition with all extras such as box, case, instruction
         manual present, but these extras not all in mint condition.
    C2 Mint condition, but without one or more of the extras.
    C3 Very minimal signs of use (first impression is that it is new,
        but careful inspection reveals a slight scratch).
    C4 Minimal signs of use (say, on the back side of an end
        plate one can see that it was used; otherwise very nice).
    C5 Signs of normal use (one-third of all slide rules are C5).
    C6 Signs of heavy use (ugly, but not damaged).
    C7 Small damage, but the rest quality C4 or better.
    C8 Damaged and well worn.

Connor Spring Co. - An American spring manufacturer that commissioned Pickett to make a specialized helical spring design slide rule called the Pickett Model 1090-ES (c1962). Connor Spring Manufacturing Company had offices at the time in Los Angeles and San Francisco, California.

Connecticut Spring Corporation - An American spring manufacturer that commissioned spring design slide rules from Pickett as well as Acu-Rule. Pickett Model 1072 (c1962)show CSC in Farmington, Connecticut. The Acu-rule version shows CSC in Hartford, Connecticut. See also Associated Spring Corp for main competitor.

Cooke Radio Rule - The 4139 Duplex was manufactured by K&E for Cooke Radio to speed up calculations for electrical and radio engineers. It has an LC scales used to determine the frequency (Kilohertz (F)) of an LC (Inductor (L) Capacitor (C)) circuit as in F=1/(2π√LC).

Copyright - "A legal device that gives the author of a work the right to control how the work is used and protects the author's expression of ideas or facts, but not the ideas or facts themselves. The life of a copyright depends on the publication date. For recent works after 1977, the life of the author plus 70 years, or if work is for hire or anonymous, then 95 to 120 years. For works during 1923 and 1977, 95 years. Works before 1923 are in the public domain." (reference: Joe Pasquale University of California). The copyright law of the United States (Title 17, U.S. Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproductions is not to be used for any purpose other than private study, scholarship, or research. If a photocopy or reproduction is used for purposes in excess of "fair use," the user may be liable for copyright infringement. Link to Cornell Law school

Cos S scale - An alternate labeling of the S scale. See S scale.

Cos Θ scale - Relative gain in coupling circuit [Pickett N16-ES Electronic slide rule].

Cox & Stevens Aircraft Corp - Mineola, NY. Made Load Adjuster and Air navigation slide rules for most US made aircraft during WWII. The Load adjuster is used to calculate the placement of ordance and personell inside an aircraft (or moments) so that the aircraft is properly balance in flight.

Cox, William - A mathematical consultant to Keuffel and Esser Co.,  invented a revolutionary slide rule construction, with scales on both the front and back surfaces of body and slide and with a double-faced indicator referring to all scales simultaneously. This Duplex slide rule was patented in 1891. The first Cox rules were made by Dennert & Pape, Germany for K&E. With the manufacture of Mannheim rules and this new rule, K&E became the first commercial manufacturer of slide rules in the United States.

Cr & Lr scale - On a Pickett N16-ES Electronic slide rule, for any frequency read at arrow on F scale, the values of resonant condensor and inductance are opposite each other on Cr and Lr scale.

Crowe Nameplate and Mfg Co. - Chicago, IL. Made aviation flight computers (circular slide rules) during WWII for the U.S. Army Air Forces.

Cruver Mfg Co. - Chicago, IL. Made aviation flight computers (circular slide rules) and aircraft panel instrument nameplates during WWII for the U.S. Army Air Forces.

CS scale - A Cosine scale found on late model Nestler Polymath slide rules. This is a separate inverse scale line, whereas most slide rule sets include the cosine reciprocal of sin on the same S scale.

CT scale - A Cotangent scale found on late model Nestler Polymath slide rules. This is a separate inverse scale line, whereas most slide rule sets include the cotangent reciprocal of tangent on the same T scale.

C-Thru Ruler Company - US company in Bloomfield, CT which made transparent rulers starting in 1939 and also made low-cost circular and linear slide rules. C-Thru continues to produce measurement and art materials.³

Cu1 - Gauge mark equivalent to √(4/πρ) = 0.1493. Note:ρ=0.0175Ωmm²/m at 20°C, ρ is the small Greek letter rho. Used for electrical calculation for copper conductors.

Cu2 - Gauge mark equivalent to √(4/πγ) = 0.1493. Note:γ=8.87g/cm³, γ is the small Greek letter gamma. g is the gravitational constant 9.81 meters/sec². Used for electrical calculation for copper conductors.

² Cube Root or 3√ scale - Cube and cube roots on the number on C or D. (Pickett).

Cubes and Cube Roots - On a Mannheim rule, with only A [B, C] D scales, cubes and cube roots as well as higher powers and roots can be found by the use of tables of logarithms and antilogarithms. On a rule with a K scale, the cube of D is found on K. The cube root of K is found on D.

Cursor - the sliding window, Runner or Indicator, with one or more hairlines used to transfer readings from one scale on the stock, or body, to another scale on the slide or stock. The cursor, perhaps invented either by Robert Bissaker or Isaac Newton, became known around 1778, in a slide rule designed by John Robertson, and the use of C and D scales for multiplication, which required the aid of an indicator to transpose calculations, had been introduced even earlier, by a British excise examiner named J. Vero (or Verie). In 1851, Victor Mayer Mannheim, introduced a transparent slab movable cursor for the slide rule of his design. Other modifications and improvements were introduced by Dennert (1886), Cox (1897), Beghin (1899), Furle (1899), Schweth (1901), Rietz (1902), Walther from the Politechnic of Darmstadt (1936). Early cursors were metal frames holding glass, followed by glass mounted on celluloid guides and spacers. Later cursors used molded acrylics or polycarbonates sliding on Teflon bearings (Dietzgen).

Cursor Scale Labels - Scale labels imprinted on the lens of the cursor. Found on 1960 and later S.I.C. (Scientific Instruments Corp) slide rules as an aid to the user. Although a unique product differentiator, no other slide rule manufacturers found it practical to implement.

Curta - A sophisticated hand-held cylindrical mechanical calculating machine made in Liechtenstein after World War II to a design by Curt Herzstark, a Austrian concentration camp inmate. It has a small crank on the top used to process the calculations. More at The Curta Page

CV - A French unit for tax horsepower, short for chevaux vapeur ("steam horses") or cheval-vapeur. CV is Metric Horsepower 1 CV = 736 watts, as compared to US mechanical horsepower of 746 Watts. CV is found on French slide rules such as the Marc(Paris)(UNIS France). In Italian ("Cavalli"), Spanish ("Caballos"), and Portuguese ("Cavalos"), 'CV' is the equivalent to the German 'PS'.

C.V. Ore - There are two known examples of a S-M slide rule labeled C.V. Ore, Harvey, Illinois with a model number of 1155. It is apparant that C.V. Ore is the person that contracted out the manufacture of this special instrument. The earlier one is a simple wooden slide rule, assumed to have been manufactured by Lawrence Engineering, as the cursor is identical to the standard models and the slide is also interchangeable . The other is a later all-plastic design assumed to be manufactured by Acu-rule or Acu-math. Both are labeled 'Copyright 1955' and have the same scales: DS [ CI-a, CI-b, C ] D, DM. The function of the S-M scales is described in the manual as: "The S-M Slide Rule is a simplified, multi purpose calculating instrument designed especially for the beginner. It contains the basic scales of professional slide rules (D, D, CI) as used by engineers for 80 to 90 percent of their work. And in addition to the basic scales the S-M slide Rule has two special purpose scales for teaching the beginner the mechanics of the slide rule and to aid him in reading conventional C, D, and CI scales." The DS and DM scales have no sub-divided divisions between the main divisions (whole numbers) on the scales. The DS scale is in 1's, the DM scale is in 10's. The C scale is the conventional numbers with divisions between the whole numbers. This may have been an easier way to learn slide rule basics.

Cycle(s) - The term cycle is used in slide rules to define one logarithmic scale is numbered from 1 to 10, such as found on the C, DCI, DI, CIF, DIF scales. A two-cycle scale or double cycle logarithmic scale is numbered 1 to 10 to 100, such as found on the A and B scales. The K scale is a three-cycle or triple logarithmic scale.

Cylindrical Slide Rule - Similar in principle to a linear slide rule, but the scales are wrapped around a cylinder. Cylindrical calculators have extra long logarithmic scales, over 60" long, and were invented by George Fuller, of Belfast, Ireland, in 1878 and Edwin Thacher, of New York, in 1881.These are the most accurate of slide rules as the scale have more divisions.




D or d hairline - Found on some European multi-lined cursors. Used in conjunction with the S hairline (may be located at the center hairline) to determine the area of a circle. Placing the D (or d) hairline over the diameter value on the C or D scale, the area of the circle is found under the S (or center) hairline on the A or B scale. Example: Position the D hairline over 4 on the D scale, read 12.6 on the A scale under the center or S hairline.

D scale - x, Principle scale used with C scale to solve multiplication and division problems. Consists of one logarithmic cycle 1-10. See C scale.

D or Q - Quality factor of capacitance or inductive circuits (capacitance will normally have some resistive factor). A coil always has some losses so Q will always equal something less than infinity [Pickett N16-ES Electronic slide rule].

D1 scale - Found on some pocket slide rules, like the Roos-108 and Post 1442, to give the same precision as a 10" long slide rule. Also C1. Not to be confused with the DI scale.

D2 scale - fx, Shifted scale, functions vary from manufacturers.

D* scale - Used in conjunction with the D scale to keep track of the decimal place in a result. Found on some Pickett slide rules. The scale ranges from 10-10 to 0 to 10+10. See Decimal keeper and Decimal Tracking

Dalton, Lt. Philip - (1903 - 1941) A United States Navy Reseve Military Scientist best known for his invention of several slide-rule flight computers the most famous being the E-6B Dead Reckoning Computer A circular slide rule with a slide used as an aid in aviation navigation and pilotage. As a graduate of Cornell University and serving as a US Naval Reserve Pilot, Dalton took an interest in slide-rule flight computers. His first models were designed in the early 1930s but it was not until 1932 that the first revision of the E-6B, originally known as the "Dalton Dead Reckoning Computer", came into existence.

Dargue Brothers - A British manufacturer that made slide rules at their Simplon Technical Instrument Works, Halifax, Yorkshire, Based on a 1934 patent.

Darmstadt - Also called System Darmstadt. An arrangement of scales originally found on German made slide rules by Aristo (D&P). Professor Alwin Walther of Darmstadt, in 1935, shifted the scales for the trigonometric functions of the slide, or tongue, onto the body of the slide rule. On the slide an exponential scale was placed along with other scales. Trigonometric scales that are dual-labeled, in black and red, with complementary angles, are considered "Darmstadt" style. In order to be called a Darmstadt, the slide rule must have a P scale and three LL scales. Scales: L, K, A, [ B, CI, C ] D, P, S, T and on back of slide: [ LL1, LL2, LL3].

Darvic - A PVC (Poly Vinyl Chloride) plastic sheet used by Blundell-Harling in their low-cost Academy slide rules.

Data Center - A slide rule designed by Sama & Etani and manufactured by Concise, Japan that incorporated a circular slide rule mounted on a rectangular sleeve that held several pull-out data cards with mathematical tables and information like the Periodic Table of the Elements. The manufacture of the Data Center that had a periodic table was discontinued, purportedly, due to complaints from teachers, who said that students were using them to cheat on exams.

Data Slide Rule - The data slide rule has only one special purpose with scales arranged in such an order to facilitate rapid sequential calculations in the particular technical field for which it is designed. Additional information in the form of tables, diagrams, pictographs, marks, arrows and formula may be supplied in order to assist the user in its operation. In the case of a regular slide rule, the user must assign the decimal point, units of measurement and the context to the scales and apply his knowledge to those tasks. Pickett, K&E, Perrygraf, Concise, IWA and others produced such slide rules and slide charts.

Date Code - A method of marking a slide rule that denotes its date of manufacture. Generally only found on upper end slide rules. This could take the form of a small, almost indiscernible, two letter year/month code pressed into the stock (Hemmi, Post) or by the use of a serial number (Hemmi, Post, K&E, Dietzgen). Later models of Aristo rules all have a manufacturing code on one edge of the rule. This is usually a combination of alpha and numeric codes which defines the rule's factory of manufacture, year of manufacture and batch number.

Dating - The method of determining the age or date of manufacture of a slide rule. Dating a slide rule becomes difficult if a manufacturer did not imprinting a date code or serial number on the stock. Even then, some manufacturers recycled their serial numbers over time, and the stock could have been left on a shelf for a period of time before the slide rule was assembled and shipped. Sometimes the copyright date in a manual is used to determine the approximate age, but one printing could span a decade. Dates that a patent was issued only suggests the first year a model may have been produced, but the patent may only refer to a certain combination of scales used over a thirty year time on different models. Having contact with the original owner of a slide rule that remembers the year it was purchased helps on determining the age. See Slide Rule Dates, Determine the Age

db scale - Decibels, Power or voltage loss in coupling circuit (ratio of voltages or power) same as extended range scale on lower stator [Pickett N16-ES Electronic slide rule].

Davis & Son - John Davis and Son (of Derby)were a British Instrument maker which made slide rules, based on D.R.P. 126499 and patent 232037. They made an improved form of the slide rule designed by V.M.A. Mannheim by engraving scales on white celluloid instead of on boxwood, directly.

DDR - Deutschen Demokratischen Republik (DDR) or German Democratic Republic (GDR). Marks slide rules as being made in East Germany, after 1949, such as the VEB Mantissa and Reiss.

Decimal Arithmetic - A prerequisite for slide rule computing. In the 18th century, decimal arithmetic (as opposed to fractional arithmetic) was more common in England than in continental Europe.

Decimal Keeper Slide Rule - A slide rule model made by Pickett with special scales to assist the user or student in keeping track of the order of magnitude of the result of a calculation. Picket models 115 Basic math and 904-ES/904-T Decimal Keeper Speed Rule use scales Marked with an asterisk(*) to perform this function. The one-sided simplex Pickett 115 has: D*, X* [ Y*, CI, C ] D, A, L scales. The 904 duplex has one side dedicated to decimal tracking: K*, A* [ B*, T*, S*, CI*, C*] D*, L* which are used with the standard scales on the front: K, A [ B, T, S, CI, C] D, L.

Decimal Tracking Cursor - A cursor that appeared generally pre-WWII on many brands including Hemmi, Post Faber-Castell, K&E and Nestler. It consisted of a small arrow that would be positioned by the user during a series of calculations to keep track of the order of magnitude of the calculated results. Typically: -10, 15, 0, +5, +10 in various increments, depending on the manufacturer.

Decimal Tracking Scale - Special scales which have range, such as -10, 15, 0, +5, +10 in various increments, that cover several log cycles. The zero is generally positioned in the center of the scale on the slide rule. Calculations are performed once with the special scales, to get the order of magnitude correct, and then with with C and D scales to get the answer to a higher degree of precision. These scales appear on a Pickett (Model 1) Deci-point and later on the more modern Pickett 115 and 904. See Decimal Keeper

Decimal Point, Determining the (Slider position method) - Where only two factors are involved, a practice is used by which the position of the decimal point in the answer can always be determined directly. Consider: 348.4 has 3 places, 0.456 has 0 places and .00678 has -2 places. Depending on whether the slider projects to the left or projects to the right, you add (multiplication) or subtract (division) the number of places for your final answer according to:
  Slider Projects to Left - Multiplication: add number of places of each factor.
  Slider Projects to Right - Multiplication: add number of places of each factor - 1.
  Slider Projects to Left - Division: subtract the difference of the number of places of each factor.
  Slider Projects to Right - Division: subtract the difference of the number of places of each factor + 1.
You will notice on some early Hemmi's in the corners a symbol like (+ | -)/(- | +). These are aids or hints for remembering how to apply the above rules: (Mult=Sum | Mult=Sum-1) / (Div=Diff | Div=Diff+1)

Decitrig  - A Decimal-Trig rule with the trigonometric scales (S, ST, T) marked in degrees and tenths of a degree rather rather than in degrees and minutes of degree.

Deci-Lon - Trademark name by K&E for their most comprehensive slide rule, with 28 scales. It was first introduced in 1962. Standard size Deci-Lon's were models model 68-1100 and the pocket version was model 68-1130. A 6 foot training version of the pocket Deci-Lon was model 68-1929.

De Leon, Oscar - (23 July 1917 - 9 Sept 1994) Founder of ODELCO, De Leon Import & Export Corporation, in the Phillipines which was incorporated in 1952. Having contacts with Sun Hemmi Japan in 1948, he became the exclusive distributer for Hemmi slide rules in the philippines. Oscar De Leon established the ODELCO subdivision around 1965, which was a community in Quezon City, and the school was named for him. Portrait 1 and Portrait 2 provided by his son, Oscar de Leon, Jr, who is the current president of ODELCO. See their corporate web page .

Deeva - Brand of plastic slide rules made in India under license by Diwa, Denmark. circa 1970. Known models: Deeva 601, Polytek 707, Teknilog 710, and Polylog 720.

Delta - Small Greek letter δ or Large Greek letter Δ.

Dempster, John (Jack) R. - (1903-1964) Designer and manufacturer of a sophisticated circular slide rule, the Dempster Rotarule, in Berkeley, California from about 1928 through 1948*. John graduated from the University of California at Berkeley in 1925 with a degree in mechanical engineering. He manufactured two models of his slide rule, starting with the model A and finishing with the model AA and produced 2500 of these slide rules from his home in Berkeley. Dempster slide rules carried some 23 scales, including 50 inch spiral C and D scales some models had surveying stadia scales. These slide rules are quite rare with some 25 known specimens in the hands of collectors. *Excerpted from "The Dempster RotaRule" by Rodger Shepherd, JOS Vol 7, No 1, Spring, 1998.

Dennert, Johann Christian - (1829-1920) co-founded of the firm Dennert & Pape (D&P) in 1862. Patented (DRP 34583) celluloid scales laminated on wood slide rules in 1886. Became the sole owner of D&P when Martin Pape died in 1884. Children Richard (1865-1924) and Jean Dennert (1869-1916) join (1869-1916) join the company as managers in 1904. J.C. Dennert worked until age 80 in 1908, died in 1920.

Dennert, George - (1900-1992) Grandson of Johann Christian Dennert, the co-founder of Dennert & Pape, and son of Richard Dennert. Became joint owner of D&P, along with his cousin Christian Dennert (1896-1944) son of Jean Dennert, after death of their parents, Jean (1916) and Richard (1924) in 1924. Created the brand name DUPA for the slide rules.

Dennert, Hans - (1926-2000) Born in Hamburg Germany to George Dennert, and great-grandson of Johann Christian Dennert, the co-founder of Dennert & Pape, later Aristo. Graduated from Darmstadt University with an engineering degree, and one year later he took over the company from his father in 1952. Aristo became one of the largest slide rule manufacturers in the world, but ceased production in 1978. Hans continued to provide assistance to slide rule collectors and was a highly sought after lecturer up until his death in 2000.

Dennert & Pape. See: Aristo.

DF scale - πx, Folded scale where every number on the D scale is multiplied by π.. DF= D x π. Note: Scale begins at π (3.14) with 1 in the middle, rather than starting at 1. For use where calculations involve π to reduce the number of settings.

DF/M scale - Scale unique to Pickett N4 Dual Base Log Log and N803 slide rules folded at 1/M=2.30, where the modulas M=log10e. See CF/M. With these scales, logarithms to base 10 may be read from the ordinary C or D scales.

DI scale - 1/x,  the reciprocal of D.

Dieterich-Post Co. - A California based, US company, founded in 1917, that currently sells modern printer, plotters, CAD media and related engineering drafting supplies. A 1949 catalog shows that they sold slide rules along with other technical equipment of the day. The slide rules looked like they were made by Hemmi in Japan. An all-plastic slide rule, labeled Dieterich-Post 3060P, was made in the USA and appears to have been produced by Charles Bruning Co. It is unclear if there was a relationship with Frederick Post Co. or if the names were coincidental. Company motto: "Builders of Goodwill".

Dietzgen - An American slide rule manufacturer, founded in 1885 by Eugene Dietzgen. The first manufacturing company opened in 1893 producing T-squares, wooden triangles, drawing boards, hectograph inks, surveying instruments, blue print and Van Dyke papers, Dietzgen's historic line of engineering products. In 1908 the company acquired its own drafting instruments factory in Germany and introduced their "Lifetime Service Policy" on drafting Instruments. The company later OEM'ed slide rules from Faber-Castell and other engineering items and drafting instruments from Germany and from Ricoh in Japan for the American Market. Often mistaken for K&E slide rules, as many parts are interchangeable as the physical dimensions and construction are similar. The main factory and head office was in Chicago, Illinois, and branch offices were in New York, San Francisco, New Orleans, Pittsburgh and Los Angeles.

Dietzgen, Eugene - (1862-1929) A German inventor, born in Uckerrath, Germany on May 6, 1862, who immigrated to America in 1878 and founded his own engineering supply house, as both a dealership and manufacturers' representative in Chicago, Illinois. The company was founded on November 13, 1885 under the name of Luhring & Dietzgen. This partnership was succeeded by Eugene Dietzgen & Co. in 1891. Successor corporation under the name of Eugene Dietzgen Co. of Illinois occurred on February 3, 1893 and the present corporate company, Eugene Dietzgen Co. of Delaware was incorporated in Delaware on October 29, 1917. He died in Chicago on December 1, 1929. His son, Joseph E. Dietzgen, continued to work in the company and had a U.S. Patent #2,369,819 issued in 1945.

Dietzgen, Joseph E. - Son of Eugene Dietzgen, founder of Eugene Dietzgen Company. Joseph E. Dietzgen, continued to work in the company after his father's death, residing in Wanatka, Illinois, and had a U.S. Patent #2,369,819 issued in 1945 for a Log Log Duplex slide rule and later U.S. Patent #2,543,313 in 1951 for a belt clip for a slide rule sleeve.

DIF scale - 1/πx, folded scale of the reciprocal of the principle scale D. See CF scale.

Digit Registering Cursor - A counter on the cursor that keeps track of the number of decimal places  when using Scientific Notation. The rules with these cursors were only produced for about 10 years in the early 20th century, principally by Faber-Castell.

Directional symbol - < - This is a Pickett innovation that is placed next to numbers (left side) on reciprocal and Log scales to inform the user that the scale is increasing numerically from right to left. This is handy on low-end slide rules that are inked all in one color, black. High end rules have the direction noted by Red Scales and K&E and others lean the numbers in the direction of increasing magnitude.

Displaced Scale - A scale may have its index placed near the middle of the the rule, which can reduce the number of movements during a calculation. Typically the A and B scale are chosen to be displaced, the distance varying by manufacturer, the most common being √10 and π.

Dividing and Numbering of Slide Rules The subdivisions of the 5 inch rule range from 50 down to 10 between the prime numbers. the 8 inch rule is divided twice as close as the 5 inch, having subdivisions ranging from 100 down to 20 between the prime numbers. The 10 inch rule, considered the standard, is subdivided the same as the 8 inch. The 20 inch rule is divided more closely than the 8 and 10 inch rules, having subdivisions ranging from 200 down to 50 between the prime numbers (text from a 1938 Dietzgen catalog).

Dividing Engine - A machine consisting of gears, used to accurately and repeatedly engrave the divisions on a slide rule. Although dividing engines were in existence in the 1700's, most slide rules were hand scribed from a master pattern using calipers to transfer the measurements, until such time as automatic machinery became popular in the late 1800's.

Division (Calculating) - In division, the divisor set on the slide is brought to the dividend on the rule, and opposite the index on the slide will be the quotient on the rule.

Divisions - The small lines, tick marks, or graduations on the scales of a slide rules that correspond to numeric values in descending decimal places. Generally, the more divisions a slide rule has the better the resolution and precision. The longest divisions, associated with the most significant digit of a number, is called the Primary, followed by the Secondary or second significant digit, then the Tertiary or third significant digit. A fourth significant digit is possible through approximation. See also Sub-divisions.

DIWA - Dansk Industri for Waterpasser A/S (Danish Industry for Levels Ltd.). A Danish manufacturer of slide rules in gentofte, Denmark. DIWA was originally began in 1854, starting as a small general store, supplying farmers in the region with a variety of items such as paint, cigars, wine, photographic equipment, tapestry, etc. In 1873 Ove Nielsen purchased the store and enlarged the business selling fuel. The third generation of Nielsens developed the area with housing, many shops, factories and a cinema. In 1924 they began making of slide rules and measuring devices in a small shop to the Danish market and to other Scandinavian countries. By 1940 they moved totally out of retailing to becoming full-time manufacturers of spirit-levels and slide rules eventually becoming Europe's leading firm in spirit-level manufacturing supplying more than half of all spirit-levels used in England. Because of war shortages, slide rule manufacture became increasingly important to their business with a 16 year partnership with Kruuse and Larsen, DIWA had experience in the complicated wood work and Kruuse/Larsen had their knowledge on scale dividing which was the basis for their collaboration.Kruuse and Larsen later went their own way and founded the company UTO. After WWII, 16 models were produced, and exported. Some sold through a Lawes Rabjohns Catalog. Students at the university and teachers' colleges in Denmark were required to use the Rietz-Ideal slide rule. Supplier to India brand Deeva. In the late 1980's the DIWA slide rules were sold by LINEX. All slide rule manufacturing stopped in the 1990's. DIWA no longer exists as a company.

Donkin and Company, Ltd - Marine engineering company (1879-1977) that started out making Steering gear registers. They had a ship's wheel as part of their logo and provided a promotional slide rule, manufacturer unknown.

DRGM - Deutches Reichs Gebrauchsmuster. Same as U.S. "registered trademark" and designs found on Aristo, Faber-Castell and other German slide rules. Equivalent to the French "marque depose". See Trademarks.

DR/DRP - German patent, Deutsches Reichs Patent. See Patents.

Dual 10"/5" Slide Rule - A slide rule which combines the convenience of the 5-inch pocket size rule with the precision of the standard 10-inch rule. One one side the C and D scales are split into the C1, C2, D1 and D2 scales which are folded at √10 (3.162). Charvoz-Roos SR-108, Post 1442 (circa 1944) and Unique Five-Ten are good examples. The Unique Ten-Twenty utilizes the same principle, turning a 10-inch rule into the equivalent 20-inch rule.

Dual Base - A rule with scales that read both common log base 10 and natural log base e of a given number.

DUPA - A trademark or brand name instituted by George Dennert after taking over the management of Dennert & Pape and used on all products between 1925 and 1936. After 1936, D&P slide rules were entirely made of plastic (Aristopal) and the slide rules were marked with the brand name of Aristo. DUPA was still used on other types of products.

Duplo - A brand name for duplex plastic slide rules made by Deeva in India. A quote from the Deeva 1720 Polylog manual: "The DUPLO Slide Rule is a delicate precision-instrument and should be treated as such. Above all protect the rule from heat over 50 C (120 F) and from direct exposure to glaring sunlight".

Duplex - An open double-faced slide rule having the area needed to have more complex scales. See Open-Body Slide Rule. Typically added three folded scales (CF, CIF, DF) to those of the Polyphase rule to make many problems easier to solve. Generally with a wrap around cursor. More advanced models having multiple cursor hairlines. Invented by the K&E mathematician, William Cox in 1891.

Duraplast - A brand name of plastic used in the construction of Staedtler Mars, a German brand of slide rules.

Dutch Circle of Slide Rule Collectors (Kring) Kring was founded in 1991 and has grown into an informal group of about 50 collectors, sharing the following goals of mutual support of members for the collecting and research and the promotion of public knowledge and awareness of the historical interest of the slide rule. These goals are pursued by issuing their periodical "MIR", by organizing meetings, presence at fairs, by publishing papers, books, catalogues, interviews and by communicating with Dutch and international communities of collectors and other interested parties. In 2004 the area of interest was expanded, and the name of the Circle was changed to Kring or Historische Rekeninstrumenten (Dutch Circle for Historical Calculating Instruments). The web site is translated into many languages.

Dynamo/Motor - %, Electrical efficiency, numbered 20 to 100, often in well of stock.




E scale - eX , Log-log scales, see LL.

E1 scale -  Same as LL2 scale, e0.1x, Exponent of x.10-1, 1.1 to 3.0, Raising to a power x>1.

E2 scale - Same as LL3 scale, ex, Exponent of x., 2.6 to 105, Raising to a power x>1.

E-6B Dead Reckoning Computer - A circular slide rule with a slide used as an aid in aviation navigation and pilotage. Originally designed by Lt Philip Dalton, USNR, the instrument was adopted by the Army Air Corps in 1942 and has appeared on the civilian market under different brand labels and variations. It was adopted for standard use by the U.S. Navy and by the U.S. Army for helicopter pilots. This slide rule is still manufactured today for student private pilots. A dead reckoning computer is a combination of two devices, one a specially designed instrument for solving wind triangles and the other a circluar slide rule for solving arithmetic problems. The E-6B calculates distance, true air and ground speed, wind direction, fuel range, pressure altitude and wind correction angles. Currently manufactured by Jeppsen, ASA and Safetech.

常数 Earth Scale - Found on the Flying Fish 1005 Stadia slide rule. 常数 on the front scale, literally means "common numbers". This scale is a useful set of constants relating to the shape and size of the earth.

Easterly, John I. - (1885-1974), born in rural Missouri became a licensed California Architect in 1926. Served two three-year hitches in the U.S. Army and fought in the Philippines. Mfg. Received his first patent in 1936 for a "Combination Square and Slide Rule" and in 1940 in Healdsburg, CA, Easterly designed the Easterly Rafter Calculator slide rule. Two wood versions were produced, along with a plastic circular model and an aluminum model by Pickett. As an architect, Easterly designed churches and schools for many years. John I. Easterly (Pop) portrait.

Easterly Rafter Calculator - Used to calculate the length of wooden rafters in building construction based on the horizontal span and rise in inches per foot. Designed and built by John I. Easterly, Mfg. of Healdsburg, CA the Easterly Rafter Calculator slide rule, around 1940. It was a wood stock model with a paper laminate with hand drawn scales and brass brackets. It was soon revised to incorporate printed scales. A circular plastic version was also made in 1955 and a later linear version, copyright 1957, with the company located in Watsonville, CA, was made by Pickett as Model 1082-ES and called the Easterly Rafter Framer.

Eckel, Arthur F. - (?-?) A.F. Eckel cofounded R.C.Pickett & A.F. Eckel Companyin 1943 with Ross C.Pickett. He was married to Myrtle Eckel, while residing in Evanston, Illinois. He left the company in 1948, which was then renamed P&E. A U.S. 1949 patent #2.466,983 was issued to A.F. Eckel with Louise Pickett being the assignee. Eckel later formed Precision Scale Company located in Phoenix, Arizona, producing all-metal slide rules to limited markets. George Washington University in Washington D.C. shows an A.F. Eckel as having graduated there in 1922. His estate sale in Phoenix produced several unfinished slide rules.

Eckel Company, The - Arcadia, CA. Made Dial-O-Matic Engineer's Log-Log circular slide rule. Presumably founded by Aurthur F Eckel but at present it is not known what the time frame was for this interprise, before or after Pickett & Eckel.

Ecobra - Bayerische Reisszeugfabrik AG, formerly Reisszeligfabrik Eichmoller & Co. An obscure German manufacturer, in Nuremberg, who made nice all aluminum slide rules, selling to Dietzgen (US) and others. Ecobra was bought out by Dietzgen in the 1970's.

Eff scale - Efficiency scale for generators and motors.

EI scale - A doubled CI scale found on Scientific Instruments Co. (SIC) circular slide rules, models 120 and 130. Where the CI scale is completed or joined together in 360 degrees, the EI scale is completed in 720 degrees, offering better interpolation of the divisions.

Electrical Slide Rules - These are used for calculating the resistance and voltage drop in conductors as well as determining the efficiency of motors and dynamos (generators). For a white paper on these slide rules, see Elektro Rules - Their use and scales by Robert Adams, presented at the 2007 Historical Calculating Instruments Conference in Holland.

Electro - A French term for an electrical slide rule.

Elektro - A German/Dutch term for an electrical slide rule.

Electronic Slide Rules - These are used for not only calculating the resistance and voltage drop in conductors, but include scales for calculating the frequency and resonance of circuits using inductors and capacitors for radio design.

Elektro - A German term for an electrical slide rule.

Elliot Brothers - Founded by William Elliott (working 1807-53). In 1850 he formed a partnership with his sons, Frederick & Charles (Elliott & Sons) and the firm became Elliott Bros from 1854. They became successors to Watkins & Hill by 1856. They produced drawing instruments and scales, including sectors) The firm eventually became part of GEC after moving progressively into electrical equipment and automation.

Embellishment Lines or E-Lines - Lines added to a slide rule scale, in parallel with the slide, so that, in combination with the divisions, a series of boxes are formed. Also called longitudal lines. Used to aid hand-engraving of the scales. This style stopped being used about 1930.

Engine-Divided Scales - Originally, the process of a machine engraving the tick marks or divisions of a scale with a knife edge, followed by filling with paint or other resin. Early premium slide rules had numbers and scales machine engraved as that puts the markings below the surface of the slide rule. Later, many top quality rules (F-C, Aristo, etc.) had scales that were impressed, ground and polished to achieve the same characteristics. Aristo and Graphoplex used a special photo-chemical process which will never wear or wash away, like the rare Aristo 940 System Güttsch. Painted or imprinted slide rules are not long lasting because the markings wear off and can be dissolved by chemical cleaners. Beware: Window cleaners with ammonia will dissolve the ink used on K&E K12's or Henschel slide rules.

Engineer - You are an engineer if you still own a slide rule and you know how to use it.

Engineering Instruments, Inc - An American manufacturer in Peru, Indiana, of low-cost painted slide rules, formed in 1947 after the marriage of Vivian C. (Lawrence) and Frank Bozarth. Vivian was given Lawrence Engineering Services as part of a divorce settlement between Vivian and George L. Lawrence, the founder of the company. Engineering Instruments ceased to exist after the building burned down in 1967.

Engineering Material - A substance that has uniform physical properties that can be calculated over temperature extremes, stress (bending) and time. Metals (aluminum, copper, magnesium, zinc, etc), Polymers (plastics, rubber, etc), Ceramics (glass, silicon nitride, silicon carbide, etc) and composites (reinforced plastics, metal matrix, fiberglass, etc.) are considered engineering materials. Some wood used for structures exhibit sufficient properties for engineering purposes.

Engineering Notation - See Scientific Notation

Engraving Machine (Kruuse and Larsen) - Two Danish partners, Kruuse and larsen (Kruuse and Larsen Instrumentfabrik) invented a logarithmic dividing (engraving) machine which made scales on wood stocks which was later employed by DIWA. The logarithmic dividing machine resembled a lathe with a horizontal moving slide on ways. A parallel clamp held the material to be engraved and a 25mm diameter spindle, located centrally along the way, was used to cut the divisions. The threads that moved the slide along the ways, was assumed to be 1" BSW having a pitch of 3.175 mm per revolution. The slides were preloaded against an axial nut by means of a wire and a pulley in the end of the apparatus with load of 20 kg hanging by the wire. At the chuck end of the lathe, a large circular disc (approximately 600 mm diameter) was mounted on the spindle. An operator turned the spindle, using a handle on the disc, making the slide move. The disc had radial markings with numbers like a protractorand moving forward by one mark resulted in moving the slide by 0.00125 mm. Another operator moved a little knife fitted above the moving slide that cut perpendicular to the movement of the slide in short strokes on the scale stock clamped to the machine. A protruding screw on the disc activated a mechanical counter, in order to count the revolutions. A table, converting the desired logarithmic scale to revolutions and marks, was created. The first operator turned the disc according to a table and kept the handle still, while the second operator moved the knife to cut the line. The second operator had a drawing close to the knife, to tell when the lines should be short and when to be long. Quite simple, but there were many errors and more than half of the scales were scrapped. Threaded spindles of that time were not supposed to have a precisely constant pitch. When errors were detected, one simply had to make a correction table. During the 1950's 90 people were employed in the DIWA factory using this machine where Kruuse acted as production manager.

Ephemera - Transitory written and printed matter not intended to be retained or preserved. The word derives from the Greek, meaning things lasting no more than a day. Some collectible ephemera are advertising trade cards, airsickness bags, bookmarks, catalogues, greeting cards, letters, pamphlets, postcards, posters, prospectuses, stock certificates, tickets and zines. In library and information science, the term ephemera describes the class of published single-sheet or single page documents which are meant to be thrown away after one use. This classification excludes simple letters and photographs with no printing on them, which are considered manuscripts or typescripts. Large academic and national libraries and museums may collect, organize, and preserve ephemera as history. (ref: Wikipedia)

Erdüs Number - The Hungarian Paul Erdüs (1913-1996, prounounced "Air-doesh") not only was one of the strangest mathematicians of the 20th century, he was also one of the most famous. He kept on publishing widely circulated papers up to a very high age and every mathematician having the honor of being a co-author to Erdüs is well respected. Not everybody got the chance to co-author a paper with Erdüs, so many people were content if they managed to publish a paper with somebody who had published a scientific paper with Erdüs. This gave rise to the so-called Erdüs numbers. An author who has jointly published with Erdüs had Erdüs number 1. An author who had not published with Erdüs but with somebody with Erdüs number 1 obtained Erdüs number 2, and so on. Similar to 'degrees of separation'.

Esser, Hermann - (1845-1908). Hermann Esser and Wilhelm J. D. Keuffel were partners in the firm of Keuffel & Esser which was founded in July 1867. The firm was incorporated in New Jersey in February 1889 and became Keuffel & Esser Company. They first manufactured surveying instruments in 1885. Hermann was born at Wuppertal-Elberfeld, Germany in 1845. He retired from Keuffel & Esser Co. in 1902. He was back in Bad Godesberg am Rheim, Germany in April of 1902 and died there in April 1908, the same year as Wilhelm Keuffel.

Estes Industries - An American manufacturer of model rocket motors and rocket kits. Vernon Estes founded Estes Industries in 1959 to make gunpowder-based model rocket motors. Members of the National Association of Rocketry (NAR) were the primary customers of Estes rocket motors which helped to inspire a generation of aerospace engineers and scientists. Retail model rocket kits soon followed and were shown in catalogs, along with computing equipment (slide rules and charts) necessary for calculating the altitude or apogee of the flights, which involved solving a basic trigonometric triangulation problem. The 1964 catalog carried Lawrence and Pickett slide rules. The Frederick Post 1447 was sold in the 1970 catalog. Estes Industries was sold in 1969 and is currently doing business as Estes Rockets. NAR 2005 Sport Rocketry Magazine Interview with Vern and Gleda Estes 5.1 MB PDF

Eucalyptus - The wood from the Eucalyptus tree, found in Australia and Brazil. Used by Australian slide rule manufacturer, W&G (White & Gillespie) for their stocks. It was well regarded because of its stable thermal properties, which resisted the temperature-induced expansion that resulted in inaccurate calculations. It is said that "If you slide the rule really quickly, you can smell the eucalyptus from the wood as it heats up."

Ewert, Artur - An engineer working for the Reiss company in Leipzig, and designed the Reiss Duplex 3227 slide rule (1965). He wrote a book "Modernes Stabrechnen" (modern use of the slide rule) which was published in Leipzig in 1969.

Evans, J.D. - c1800's. Dr. J.D. Evans described a grid-iron slide rule in 1866. This was the earliest form of a long scale slide rule, whereby the length is increased by having multiple portions of the scale in a grid.

Everard, Thomas In an English Excise officer of the Excise [tax], was designing rules specifically for the measurement of the content of various vessels and containers. In addition he added scales for the direct computation of square and cube roots. In 1775, Everard, inverted the logarithmic scale and adapted the slide rule to gauging. These rules, usually square in section with a slide on each face, were made by instrument makers such as Stutchbury, Roberts and Bate, and were probably the first commercially available slide rules, those made earlier were by private commission. It is Everard who is credited with introducing the term "sliding rule", later being abbreviated to slide rule.

Evolution of Scales - Over 300 years, the orientation, position and sequence of using the scales on a slide rule became more refined which made it easier to perform calculations in less steps. (Note: Evolution in this sense properly means that intelligence was added to the equation to make things better. Consequently, the term 'Evolution' from a biological standpoint is a misnomer, since everything dies off and becomes extinct, unless intelligence is added to the mix.) See Pickett Scale Evolution:

Extended Length Slide Rule - See 20 Inch Slide Rule.

Extended scales - Tick marks that extend on either end of the normal indices which help to speed up calculations. Some models change the color of the extended part of the scale to differentiate from the standard scale length.

Eye-Saver 5600 - Eye-Saver Yellow green (Angstrom 5600), the distinct yellow that is identified with Pickett slide rules, which was promoted as a help to prevent eye-strain headaches, to improve slide rule computation speed and accuracy, to reduce error and lower costs. Chromatic aberration tests by Pickett established that Angstrom "5600" is the point on the spectrum for optimum eye-ease. Pickett Eye-Saver yellow green exactly duplicates this color value. Eye-Saver "5600" reflects long wave length rays, while white reflects all colors, including the short wave length actinic rays, which create "hot" spots and the contrast with the graduations is supposed to improve precision in reading the graduations. The -ES option was available on all models of Pickett All-Metal and plastic slide rules.




f or F scale - frequency, for electrical and radio calculations. Prior to 1965, these numbers would be in cycles per second, rather than Hertz.

Faber-Castell - German manufacturer of slide rules, starting in 1892, that began as A.W. Faber pencil factory as early as 1761. Slide rules started out as boxwood, with celluloid facings added in 1897. English manuals were translated by C.N. Pickworth for American distributor in Newark, New Jersey, USA. In 1905, the name was changed to Faber-Castell. Celluloid laminated mahogany was used from 1902 to 1912, followed by celluloid faced Pearwood. In 1952 all-plastic (Geroplast) versions were introduced. The duplex slide rules began in 1961. The most complex slide rule was the multi-colored Novo Duplex 2/83N. Faber-Castell still has factories in Germany and distribution houses in over most of the world. See expanded Faber-Castell timeline.

Fabrikoid - A vinyl coated fabric used to make protective sleeves, typically for Gilson circular slide rules, similar to Naugahyde, having the external appearance of leather.

Factor of safety (FoS) - also known as Safety Factor, is a multiplier applied to the calculated maximum load (force, torque, bending moment or a combination) to which a component or assembly will be subjected. Thus, by effectively "over engineering" the design by strengthening components or including redundant systems, a Factor of Safety accounts for imperfections in materials, flaws in assembly, material degradation, and uncertainty in load estimates. An alternative way to use the safety factor is to derate the strength of the material to get a "design" strength. (Ref:

Fagen, Daniel W. - Purchased the Gilson Slide Rule Company, Stuart, Florida, in 1960 from Clair Gilson. Fagen was an ex-machinist and operated a moving and storage business in Stuart, Florida delivering metal stock and supplies to Gilson Slide Rule in the 1950s. Fagen befriended Clair Gilson and when Clair's health was failing, offered to buy the company. Unfortunately Gilson died before he was able to explain all of the manufacturing processes to Fagen. Fagen moved the machinery into a storage warehouse and worked out all of the manufacturing and mathematical details on his own. The 1920 vintage screw machines and punch-presses used to make the Gilson slide rules were operated off of a multiple clutched pulley and belt system which required considerable maintenance. Fagen's son, Daniel II, said his father had to make many of the parts to keep the machines running. Fagen sold the company in the early 70's. Fagen history contributed by son,  Daniel Fagen II.

Farmar, Frank C. - (c1840) Farmar and Sons, Liverpool, England, made boxwood slide rules for brewers who sold or distributed wine and spirits (distilled liquors) to determine the excise taxes for publicans (accountants). In his instruction manual of January 1902, Farmar wrote "For many years past traders have unceasingly complained of the old unsatisfactory rules hitherto in use -- rules which suited their forefathers, but which no longer meet modern rquirements; and it was felt that steps should be taken to remedy this state of things. Accordingly, in 1900, I was invited to co-operate with a representative committee of the ablest and most up-to-date men in the trade, with the result that this long wished for rule was at last produced. It is thus brought abreast with the times, and represents the first really beneficial change made in the slide-rule for 100 years."

Farmar's Rule - A specialized slide rule, designed by Frank C. Farmer (c1900) for tradesmen in England who sold or distributed wine and spirits (distilled liquors). The A and B scales on the front, and the G and H scales on the back, are conventional two-decade logarithmic scales -- i.e., the conventional A and B scales. The C scale is used in conjunction with either D, E, or F to compute the amount of liquid in a barrel. The G and H scales are used in conjunction with the Reducing scale to compute the amount of water to add to a given amount of spirits to reduce it's proof (alcohol content) to a desired amount, or the amount of spirits that must be added to raise the proof. The I and J scales are used together to compute the change in value of spirits if the proof is raised or lowered. The I and K scales are used together to calculate profits or discounts on sales; similarly the I and KK scales are used together to calculate profits or discounts on costs.

Felsenthal Instruments Co. - (G. Felsenthal & Sons, Chicago, Illinois) Maker of Aviation Flight Computers according to US Military Specifications, both in aluminum and plastic. During World War II, Felsenthal produced over 75% of the plastic calculating instruments used by the Army Air Forces, and over 90% of those used by the Navy Bureau of Aeronautics. In the post-war period, it introduced a variety of plastic items for commercial and technical purposes. This firm was located in Chicago. It was known as G. Felsenthal & Sons in the 1940s, G. Felsenthal & Sons, Inc. in the 1950s, Felsenthal Plastics Inc. in 1971, and Felsenthal Instrument Co. in 1972.

Fermi, Enrico - In 1943, Nobel Laureate Enrico Fermi used a K&E pocket slide rule to control the stages of the world's first self-sustaining nuclear chain reaction, beneath the stands of Stagg Field at the University Of Chicago. As assistants stood by, Fermi used his rule to determine the amounts by which the cadmium control rods were to be withdrawn from the pile of graphite and enriched uranium.

Festus Mfg. Co. - (1938-39) located in Festus, Missouri. An American manufacturer founded by Paul Jones Jr. Festus made low-end wood slide rules, as well as window and door frames. Festus became the Acu-Rule Mfg Co. in 1940 and relocated to St. Louis, MO using the brand name of Acu-math. Paul Jones Jr. died in 1945. See A Short History of the Festus Manufacturing Company by Geo. E. Keane

Filotecnica Salmoiraghi - Italian company that made optical instruments. Filotecnica (translated from Italian to English means: "Loving the Technic") was funded in 1865 by Ignazio Porro. Porro was mainly a surveyor, but his name is linked to invention of binoculars, based on Porro's prism. Filotecnica was basically a school with a laboratory, producing just special prototypes. After few years Angelo Salmoiraghi, a pupil of Porro in Milan Politecnico, transformed Filotecnica in an industrial company and the name became Filotecnica-Salmoiraghi. The logo IAS (Ingegner Angelo Salmoiraghi) was often used as well. Production covered all kinds of precision devices: surveying instruments, optics, harmonic analyzers, avionics, drawings tools, sewing machines, ... slide rules. Of particular interest was a projection slide rule which used two back lighted glass disks to project the scales on a screen. After 1970 circa production ceased and now Salmoiraghi-Viganò is just the largest Italian reseller of spectacles and sunglasses.(notes courtesy of Anrea Celli, Italy - ISRG). More at: Link

Financial Slide Rule - A type of rule, used in commerce, having scales to easily calculate profit, loss, mark-up, discount, amortization, interest, inventory, etc. The allocation of the standard scales are sometimes labeled on the right hand side for convenience. On a German Faber-Castell Commerce rule the scales are labeled : E (Einkauf - Purchase), V (Verkauf - Sale), T (time), Z (interest) and K (capital).

Fisher Governor Company - A U.S. company supplying control valves for the gas, steam and high-pressure-air industry out of Marshal Town, Iowa. They commissioned Pickett, and possibly Acu-Rule, to make specialized slide rules for sizing applications of their equipment. Known copyrights are 1954 and 1967.

Flying Fish - A Chinese slide rule factory and brand of slide rules that were manufactured in Shanghia, China. An earlier name of the factory was Shanghai Ding Feng which was a joint private-state owned factory.

Folded Scale - A scale that has the '1' somewhere in the middle of the scale, with the end starting at a point convenient for making quick calculations, such as the CF and DF scales are folded at π (3.14 or pi). Also used to minimize the distance of the stroke of the slider.

Fowler's calculator - Fowler (Manchester, England) was best known for making pocket watch style calculators. These were originally named "Mechanical Engineers". Fowler was originally a publishing company, "Scientific Publishing Company", selling engineering handbooks and a weekly magazine called "The Mechanical Engineer". That became kind of a brand name for them, as they also sold the calculators and a chronograph pocket watch under it. One face has a long-scale and short-scale logarithmic scale. The short scale could be used for rapid calculations or as a check that the correct sector of the long scale had been used. The other face has a short-scale and reciprocals, logs, square roots, sin, tan and sin-tan scales.

Frankreich - Seen on some German Slide rules made in France during WWII, like Damien Maurice. In German, France is still called Frankreich, which literally means "Realm of the Franks". In order to distinguish from the Frankish Empire of Charlemagne, Modern France is called Frankreich, while the Frankish Realm is called Frankenreich.

Frederick Post Company - U.S. Manufacturer and distributor of slide rules. See POST.

Fundamental Scales - x - Also called Primary Scales. Located on the body as D and on the slide as C. Typically the first variable of a calculation and upon which all other scales are mathematically calculated.

Function - A function, in mathematics, is a "rule" that assigns a unique output to each given input.

Fuji - Fujikeiko Co. Japan, est. 1949, became Fuji Slide Rule Manufacturing Co Ltd They sold under their own brand as well an OEM supplier for Wolters-Nordhoff in Holland. Their all-plastic slide rules sport a light green accent.

Fuller, George, M. Inst. C.E> - (???? - ????) Ireland. Professor of (Civil) Engineering at the Queen's College (now University of) Belfast in Northern Ireland. who designed the Fuller cylindrical slide rule with spiral scales in 1878. It was patented as an "Improvement in Calculators" in 1879. Its remarkable length permitted a high level of precision in calculations; calculations could be made to 4 or 5 significant digits. The principal manufacturer of these slide rules was W. F. Stanley Hall of London, who possessed the necessary dividing engine for such an undertaking. It was marketed by Keuffel and Esser Co. in New York from 1895 to 1927. Stanley continued its production until 1972, as until the introduction of the electronic calculator, it was preferred by astronomers and scientists.

Fuller Spiral Slide Rule - Designed in 1878 by Professor George Fuller, the logarithmic line is arranged spirally on the surface of a cylinder. By means of movable cylinders any length of spiral line may be at once transferred to any other part of the scale, and multiplications and divisions containing a series of factors can be worked with facility. Logarithms of numbers are given by means of a scale on the longer index arm together with a circular scale on the first cylinder, so that powers and roots are obtainable. The surface of the middle cylinder bears printed tables of decimal equivalents, natural sines, etc. The axis is provided with a handle for the hand or for mounting onto a fixed base. On the cylinder is a logarithmic scale that spirals along the cylinder, having the equivalent length of 500 inches with 7,250 divisions. In comparison, a standard 10 inch slide rule has about 160 divisions. Sold by numerous slide rule distributors, one example being Dietzgen model 1794. . More info

F. Weber & Company - See Weber, F., & Co

Fullerton Engineering Sales Co. - A rebranded reseller of Acu-math slide rules located at 4623 York Blvd. Los Angeles 41, California, phone: Clinton 6-2286. the telephone number dates the company in the 1960's. A Concise 28N circular slide rule re-branded as Fullerton No.1450 showed an address for Fullerton Sales Company, 811 Milford Street, Glendale 3, California. Telephone 245-7261.




g - Gauge mark for the gravitational constant gF = 9.81 meters/sec² equivalent to gE = 32.2 feet/sec². (Be sure to check if your slide rule is using metric or Yankee units).

Gθ scale - "Gudermanian" scale gives the hyperbolic angle, sinh θ found on T scale and tanh found on P scale (Hemmi/Post).

Galileo Galilei - (1564-1642) Popularized the sector at the very end of the 16th Century. The sector is a graduated ruler that uses trigonometric formulae and a caliper to calculate squares, cubes, reciprocals and tangents of numbers. Galileo's design of the sector as a mathematical tool can be seen as the moment when calculation aids cease to be based upon counting and instead exploit the deeper relationships among numbers. His invention is still in use as a navigation aid in the 20th century 300 years later.

Gamma or γ - The small Greek letter γ.

Gamma - A Hungarian slide rule manufacturer out of Budapest.

Gauge Mark or Gauge Point - Constants or numbers which are used to frequently in calculations marked on the scales of a slide rule to save the user save time by not having to remember the constant or by minimizing repetitive calculations. The most common gauge points are found at 3.14, representing pi, and .785 representing pi/4. See π/4.

Geek - A person who has chosen concentration rather than conformity; one who pursues skill (especially technical skill) and imagination, not mainstream social acceptance. As the mainstream culture becomes more dependent on technology and technical skill, mainstream attitudes have tended to shift towards grudging respect of Geeks. Quote "Old Geeks never die, they just collect slide rules", Mike Konshak, circa 2000.

Geniac - The Geniac brand cylindrical slide rule sold by Oliver Garfield Company in New York was initially a relabelled Otis King made by Carbic Ltd in England. Garfield later made his own, probably unauthorized version of the Otis King (around 1959). The UK patents covering the mechanical device(s) would have expired in about 1941-2 (i.e. 20 years after filing of the patent) but copyright in the drawings would typically only expire 70 years after the author's death.

Geotec - A brand of Canadian slide rules, presumed to be a spin-off company of Hughes-Owens, as they have matching model numbers to H-O slide rules. Geotec slide rule were manufactured primarily by the Japanese company Sun Hemmi.

Gerber, Joseph H. - (1924-1996) United States. Inventor/businessman. Gerber, a holocaust survivor, immigrated to Hartford, Conn., from Austria in 1940, and completed high school in two years while working full time. Gerber's first patented invention was the Gerber Variable Scale, which he conceived in 1945 while he was a college student at Rensselaer Polytechnic Institute, graduating in 1947. He built the product in his garage. Leaving his job a few years after graduating, he drove around America for months at a time to visit engineering departments of military and industrial organizations. He sold his existing products by day, and invented new ones at night. It was the first product to launch the Gerber Scientific Instrument Co. Gerber, who held nearly 650 patents, was awarded the National Medal of Technology in 1994, given to him by U.S. President Bill Clinton. Several of his inventions are on display at the Smithsonian Institution. The story behind his invention The Inventor's Dilemma: The Remarkable Life of H. Joseph Gerber was written by his son, David J. Gerber. (Yale University Press, 2015)

Gerber Scientific Instrument Co. - The business began as the Gerber Scientific Instrument Co., founded in 1948 by Austria native Joseph Gerber to support his invention of a variable scale slide rule, the first of 675 patents he'd eventually hold. The Gerber Scientific Inc., located in Tolland, Connecticut, is the parent of companies that supply software and hardware systems for apparel and technical textiles, sign making and specialty graphics, composites and packaging applications. It is currently owned by by Vector Capital, a San Francisco-based, global private equity firm specializing in the technology sector.

German Slide Rule Brands - Slide rules manufactured or re-branded by major German companies (including DDR) were A.W. Castell, Faber-Castell, Nestler, Dennert-Pape, Aristo, Eco-Bra, Friedmann, H-H Universum, Meissner, Reiss, Rista, Staedtler, Staedtler-Mars, Veb Mantissa, (list incomplete).

Geroplast - The proprietary name for the plastic (Polystyrol-Butadien) used in modern era German Faber-Castell slide rules. Faber-Castell recommended the use of their Geropur cleaning solution for restoring the stock. Some OEM slide rules had a prefix of "G" (such as Dietzgen G-1734) which denoted the material.

Giken - A Japanese manufacturer of all-plastic slide rules, thought to be the predecessor to Fuji. Giken had the same location as Fiji, but had a line of slide rules in 1963 that shows no overlap with Fuji models that appeared in a Fuji price list printed in 1970. ref: William Lise.

Gilson, Claire A. - (? - 1960) Founded the Gilson Slide Rule Co. in 1915, in Niles, Michigan. His first circular slide rule was printed paper glued to a 4" diameter steel disk. He purchased the Richardson's Rule Works, approximately in 1919, from George W. Richardson, presumably to obtain the printing process for scales used on Richardson Rules. The family relocated to a small island near Stuart, Florida, after 1927. The founder's son, Richard A. Gilson, computed the scales for the Gilson Atlas while still a teenager. The company was sold in in 1960 to Daniel W. Fagen. Clair died that same year.

Gilson Slide Rule Company - Made circular metal slide rules, est. 1915 by Claire Gilson in Niles, Michigan. OEM's to many other manufacturers' brands as Atlas, Midget, Post, Lietz, Dietzgen, Bruning and Travella. Gilson bought Richardson Rule Works prior to 1920. It was a good match as Richardson's printing process for the scales, black paint on metal, appeared in the second version of the Gilson Midget Slide rule, Copyrighted 1919, patent dated 1-17-22. Manuals from both companies used Richardson's "Be Wise" Owl in the manuals. The Gilson name never appeared on any of their slide rules. Known Circular models were the Gilson Binary, The Midget (several variations), Apex, Commercial, and the Atlas. While the others used concentric scales, the Atlas had a spiral scale equivalent to 75 feet in length. The founder's son, Richard A. Gilson, computed the scales for the Atlas when he was a teenager. Other special purpose slide rules were created. Claire Gilson was unable to continue the business because of illness and sold it in 1960 to Daniel W. Fagen, a local machinist and owner of a moving and storage business. Fagen manufactured Gilson Slide Rules in Stuart, FL until the early 1970's, when the company was sold again. The last owner had neither the machining or mathematical skills to continue the business and the purchase was ill-timed with the advent of the electronic calculator. Fagen history contributed by son, Daniel Fagen II.

GIW Hydraulic Slide Rule - Also known as the Pickett N15-T. In 1960, Danforth W. Hagler, who's family ran Georgia Iron Works, Grovetown, Ga., conceived and designed the GIW Hydraulic Slide Rule. Before its invention, each engineer in the engineering department had a large, thick notebook with about 100 pages of graphs. The slide rule incorporated many hydraulic pump and pipeline formulas. One side of the slide rule contained engineering formulas involved with performance of a pump while the other side contained everything necessary for pipeline and production calculations. GIW is now a subsidery of KSB Aktiengesellschaft.

Gong Si He Ying - means "joint state-private ownership" and is found on sleeves of Shanghai Ding Feng (later Flying Fish) slide rules. In China, any enterprise with the words "Gong Si He Ying" existed only for a short period in the 1950's. The PRC (Peoples Republic of China) was founded in 1949. Before that time, there were quit a few privately owned businesses in China. In the beginning of the PRC, after suffering through the Japanese invasion of WWII and later the Chinese Civil War, the Communist State had a difficult time obtaining capital for business, but slowly every thing was restored. In rural communities, farmers received farmland that been confiscated from landlords and in cities or towns, enterprises needed funding and technical support. The communist government, rather than confiscating the enterprises that were privately held, wisely decided to jointly administer many enterprises between the state and private companies, putting the words "Gong Si He Ying"on front of the enterprise or company name. However, by the 1960's, when prosperity had increased, the "joint state-private ownership" enterprises were gradually absorbed into only state run companies. Up to 1978, no private funding or ownership was allowed in manufacturing, commerce, or any enterprise. Since 1978, many private run enterprise are growing rapidly in China, including many "joint state-private ownership" enterprises, the words "Gong Si He Ying" are not used on the front of name. Contributed by Liu Ql in Beijing, China

Gottheimer, Abel and Ethel R. - Abel (1891-1979 - died Nassau, NY) and Ethel (?-1979) Gottheimer founded the Roos Company of 280 Madison Ave., New York, in a partnership with Andre and Angele Charvoz, circa 1941, manufacturing painted wood and laminated wood slide rules, presumably to fill the void caused by import restrictions during WWII. A reasonable assumption was that Gottheimer manufactured the slide rules and Charvoz handled marketing, as by 1945, The Roos Company was distributing "Charvos" [sic] drawing instruments manufactured by Andre Charvoz, under Charvoz, Inc. The Roos Company and Charvoz Inc. were merged into Charvoz-Roos Corporation in 1946.

Graduations - The small lines or tick marks engraved in the surface of a slide rule, the major or primary graduations labeled by numbers corresponding to the value of the divisions of the scale.

Graphoplex - A French manufacturer of slide rules that also supplied slide rules for Koh-I-Noor, a European company, still in business, with subsidiaries in the USA.

Gravet-Lenoir - (c1830) French manufacturer of slide rules in Paris.

Green, Alex E.S. - (1919-) Graduate Research Professor Emeritus at the University of Florida. During WWII, as a B-29 crew member, Dr. Green designed several slide rules which were used by the U.S. Military. The first "Ship length Computer" was an idea that came from a discussion with another aviator on the difficulty of identifying ships. Green's slide rule was designed to be used with the B-29 gun sights. This was used to identify the elusive Japanese battleship Yamoto. During this mission, which located the hidden Japanese fleet, which had run out of oil, the B-29 itself ran out of gas and had to make a forced landing in Xian, China. This event led Green to create the "flight Engineer's Computer" to minimize gasoline consumption on long over-water missions. Alex Green was awarded the Medal of Freedom in 1947. Currently researching thermal waste to energy conversion at U. of F. and a fellow of the Oughtred Society. Biographic article in Physics Today, 2001

Grid-Iron - A form of construction of long scale slide rules, taking the name from the grid of scales which make up the total scale length. See Evans, J.D.

Grooved Guide - The joint between the body (stator) of a slide rule and the center slide which retains the slide during manipulation. All linear slide rules incorporate some form of grooved guide to capture the slide. Some slide rules designs provide an adjustment of the clearance of the guide to improve the feel and alignment to maintain the precision of the movement.

Ground Water Hydrology Computer - Designed by N. Thomas Sheahan in 1967 while employed by Layne Associates, Research Division, Memphis, TN, a ground water development firm that drilled wells, as a Research Geologist. This circular slide rule, constructed using 4 disks, was used to solve the complex equations for flow of ground water in the subsurface, which was otherwise a tedious and difficult calculation (before computers). The slide rule allowed hydrogeologists to calculate the flow of water from wells, the characteristics of the ground-water-bearing formations (aquifers), and the effects on the environment from pumping ground water. It replaced a nomograph which involved tedious and time consuming calculations. About 1,000 of the circular Ground Water Hydrology Calculator slide rules were produced by Info, Inc., Newton, MA.

Guedon - US manufacturer located in Camden, New Jersey and Schenectady, N.Y. Their celluloid pocket slide rules were made in France by Unis, and their sheet metal pocket slide rule was made in Camden, NJ.

Gunter, Edmund - (London, England, 1581 - 1626), plotted logarithms on a two-foot straight line (the Gunter Scale) in 1620. The positions of numbers were proportional to their logs which graphically represented the work of John Napier. With such scales, multiplication and divi sion were performed by addition and subtraction of lengths by a pair of dividers. In 1623 he published a description of this scale that is composed of two scales of the logarithms from I to 10 placed end to end. Although Napier conceived of the logarithm allowing multiplication or division to be accomplished by addition or subtraction, Napier relied on look up tables. See Edmund Gunter at

Gunter Rule - The calculating device created by Edmund Gunter that was to be the predecessor of the modern slide rule. A pair of dividers is used to measure a distance (the multiplicand and the multiplier) along the rule and add it to another distance, the multiplicand, forming the combined distance, the product, on the rule. The accuracy of an answer is limited by the length of the rule and the user's ability to resolve a number.

gwr - A mark found on military slide rules manufactured by Hamburg based German maker Dennert & Pape (later Aristo), used during WWII 1942-1945. During WWII, suppliers of instruments, like slide rules, to the German Armed Forces were not allowed to show/advertise their company name or logo. Such WWII codes double-up as a useful dating guide.

G-W Photo Slide Rule - A slide rule specifically oriented to photographers to aid in determining settings for flash lamps and focus. G-W are the last initials of both inventors, C.G. Goodchild and L.V. Whitney, both PhD's. One example was manufactured by Acu-Rule for AREL Inc, St. Louis, MO.




H scale - 2x, a double scale H = 2 x D.

H1 scale - √(1+x²), Hyperbolic scale, range 1.005 to 1.5

H2 scale - √(1+x²), Hyperbolic scale, range 1.4 to 10

Hairline - The sharp thin vertical lines on the inside of the cursor window or glass. These were either etched or silk screened on. Originally, before glass and plastic windows were added to cursor frames, an actual horse hair was stretched across the cursor frame in open air and tightened with screws. Some more modern cursors have multiple hairlines as an aid in conversions and calculations - see Multi-Lined Cursor

Hairy Eared Engineer - 1) An engineer who's old enough to have hair growing out of undesirable places. 2) ...has been practicing engineering so long that he or she has already made all possible mistakes at least once. 3) A desirable person to have on a project to ensure the mission succeeds. 4) Quote: "Every project needs at least one hairy-eared engineer" Marvin B. Davis - Circa1980.

Hagler, Danforth W - In 1960, Designed the Georgia Iron Works Hydraulic Slide Rule which was Pickett's Model N15-T. See GIW.

Halden Calculex - A circular slide rule in the form of a 2-3/8 inch diameter pocket watch. It consists of two concentric metal discs, graduated in the same manner as a linear slide rule, with two glass covers, which act as cursors on each side. Was sold as a Dietzgen 1795A, a Frederick Post 1448 and others.

Halden, Joseph - Founded Joseph Halden & Company after being in partnership with Alexander G Thornton from 1878 at 8 Albert Square, Manchester. Joseph Halden set up an independent firm at the same address when A.G. Thornton left and was an important manufacturer of both drawing and surveying instruments and had factory works at various addresses around Manchester and branches in many other cities. The Halden Calculex was distributed by A.G. Thorton. Joseph Halden retired in 1892 and his son J.L. Halden took over the business. J.L. Halden died in 1965. Joseph Halden & Co. was taken over by the Ozalid group in 1969. More Halden history courtesy of Museum of Science and Industry Manchester, England.

Hand Scribed - Most slide rules, prior to 1890, were hand scribed from a master pattern using calipers to transfer the measurements, until such time as automatic dividing engines became economical for manufacturing.

Harling, W.H. - London manufacturer, est. 1851, purchased by Blundell in 1966 forming Blundell-Harling.

Hartung, Prof. Maurice Leslie - (1902 - 1969?) studied Mathematics at Cornell College, Iowa. In September 1926 was accepted as a member of the American Mathematical Society. Hij received his PhD in 1931 from the University of Wisconsin for his thesis "On a Family of Integral Equations with Discontinuous Kernels". In 1977 received the Distinguished Life Achievement Award of the Illinois Council of Teachers of Mathematics. He wrote most of the manuals for Pickett slide rules and may have been the inventor of the DFM and DF/M scales.

Heinlein, Robert A. - (1907-1988)American science fiction author. A character in one of his novels states: "Dad says that anyone who can't use a slide rule is a cultural illiterate and should not be allowed to vote. Mine is a beauty - a K&E 20-inch Log-log Duplex Decitrig" Have Space Suit - Will Travel 1958.

Helical Scale - A method of extending the scale length used on tubular or cylindrical slide rules, such as Otis and Fuller. The scale is wrapped as a helix around the tube's diameter thus enabling many feet of scale over a small length.

Hemmi - Hemmi Bamboo Slide Rule Company Ltd. in Japan is the oldest and most well known Japanese manufacturing company making slide rules. Jiro Hemmi (1878-1950) and Company was founded in 1895 and, in 1912, was granted by the Japanese Patent Office Patent No. 22129 for their laminated bamboo construction method for slide rules. As a young company wanting exposure to a larger market, They started by selling distribution licenses to three other companies: the Fredrick Post Company of Chicago, Illinois, the Hughes-Owen Company of Canada and Tamaya & Company of Tokyo, Japan. Tamaya, an already a well-established and well-known firm in Japan, began selling Hemmi Slide Rules in 1913. The Hughes-Owen Company of Canada (another old firm), began selling the Hemmi Slide Rules in Canada in 1914 and in 1931, the Fredrick Post Company, of Chicago, Illinois, began selling them in the United States. All of three of these companies were selling Hemmi-manufactured Slide Rules under their own and Hemmi's name. Sun Hemmi also supplied re-branded OEM slide rules to other North American companies like US Blueprint, Lafayette, Lietz, and Geotec (a Hughes-Owens brand). Early examples may have had the "Made in Japan" or "Made in Occupied Japan" sanded off due to anti-Japanese sentiments after WWII. It is estimated that Hemmi produced about 15 million slide rules altogether. See Pre-1940 Hemmi Manufacturing Process

Hemmi, Jiro - (November 1878 - April 4, 1953) The father of Japanese slide rules. Co-Founder of Sun Hemmi Slide Rule with Hisashi Okura, later renamed Hemmi Keisanjaku KK (Hemmi Slide Rule). Jiro Hemmi graduated in 1890 from primary school in Chiba Prefecture. In 1893 he worked for Nakamura Surveying Instruments in as a reduction scale worker then struck out on his own in March, 1899 to manage a business making slide rules as Sun Hemmi. He started to study slide rule fabrication at age 17 (1895). Slide rules dimensions tend to change and scales to lose their accuracy due to the great variations in meteorological conditions between seasons in Japan, particularly to high temperature and humidity in summer. To deal with these problems, Jiro Hemmi made a great number of prototypes with different woods, such as cherry, boxwood, quince and mahogany. After many tries, Jiro Hemmi made his first slide rule using Moso bamboo plywood, a species of bamboo found mainly in Japan.He got passionate about his work, and when he was asked to make copies of a Mannheim slide rule, he was already the best scale maker of his time in Japan. In 1912, Jiro obtained a patent for the method to make slide rule with no defect using treated moso bamboo, followed by patents in England and France (1917), and in the United States, China and Canada in 1920. In 1917 the SUN mark is established as the Hemmi trademark. Being the symbol of Japan itself, A fire badly damaged the wooden house used by Jiro Hemmi as a shop and workshop in Sarugaku district in Tokyo in 1924. Hisashi Okura, an expert in international trade, visited Jiro Hemmi, who was in a difficult situation because of the fire, and offered to participate in the business management. They founded the Hemmi Workshop as a partnership company in 1928. They worked together to differentiate Japanese slide rules from those built in the US and Germany. In 1933 Hemmi Worksop became a limited company. During the Second World War, Hemmi made slide rules used for battleship artillery calculations and to design the battleship Yamato. Jiro retired from Hemmi Slide Rule in 1941 for health reasons.

Henschel Co. - John Henschel Co. Inc. Circa 1945-1980. In 1959 the American company was located at 105 E. 29th St. in New York City, NY. Sold slide rules, drafting supplies under its brand. Also manufactured Pelikan Fount India Ink for fountain pens and typewriter ribbons. A 1979 American Medical Assn© Journal mentions John Henschel Co. of 14 Albertson Avenue, Albertson, NY as a supplier of biological inks for testing stroke victims. The construction methods of known duplex slide rule samples indicate that may have been manufactured by Charvos-Roos with scales designed by Acu-Design, which is associated with Acu-rule/Acu-Math slide rules. Its possible that the scales were applied onto the stock and slide using a heat-transfer method, which became popular in 1950 (called Thermofax) and unlike engine-divided scales, the numbers and divisions are easily wiped off with a strong cleaner like Windex Ammonia-D. Colored inks did work as well as black copied by heat-transfer. Other similar slide rules can be found under the Frederick Post and Charvoz-Roos brands.

Herwijnen, Herman van - (1929-2004) Avid Dutch slide rule collector and author of the Slide Rule Catalogue© and co-author of Calculating on Slide Rule and Disc with IJzebrand Schuitema. Married to Diny van Herwijnen. Member of the Dutch Circle of Slide Rule Collectors Graduated with Mechanical Engineering degree from Technical University Delft in 1954. Spent two years in the Dutch Air Force followed by 13 years woking in Venezuala for Dutch Royal Shell. Had his own firm, Infro Software, and lectured at Shell and Technical University Delft up until his death. Herman last attended the IM 2003 Swap Meet

Historical Developments in the Evolution of the Slide Rule. - from a 1962 A.G. Thornton slide rule instruction manual with additions. See Slide Rule History.
1614 - Invention of logarithms by John Napier, Baron of Merchiston, Scotland.
1617 - Developments of logarithms 'to base 10' by Henry Briggs, Professor of Mathematics, Oxford University.
1620 - Interpretation of logarithmic scale form by Edmund Gunter, Professor of Astronomy, London.
é 1630 - Invention of the slide rule by the Reverend William Oughtred, London.
1657 - Development of the moving slide/fixed stock principle by Seth Partridge, Surveyor and Mathematician, England.
1775 - Development of the slide rule cursor by John Robertson of the Royal Academy.
1815 - Invention of the log log scale principle by P.M. Roget of France.
1850 - Amédée Mannheim, France, produced the modern arrangement of scales.
1886 - Dennert & Pape, Germany, introduce white celluloid as a material for inscription of scales.
1890 - William Cox of the United States patented the duplex slide rule. 1900 - re-introduction of log log scales by Professor Perry, Royal College of Science, London.
c1900 - Engine divided scales on celluloid increases precision of slide rules.
1933 - PIC Differential trigonometric and log log scales invented by Hubert Boardman, Radcliffe, Lancashire.
1976 - The final slide rule made by K&E donated to the Smithsonian Institute, Washington, DC, USA.

Hoffman - A Danish manufacturer of UTO slide rules for the OEM promotional slide rule market.

Holophane Calculator - A specialized slide rule used for calculating illumination angles and properties of holophane lamps. Produced by Blundel, Luton, England. Circa 1950.

Hope - A Japanese (Tokyo) slide rule manufacturer that also supplied OEM products to other companies such as Jakar. Hope Slide Rule Mfg. Co., Ltd. Shigets Building, No. 26-18, Asakusabashi, 2-chome, Taito-ku, Tokyo, 111· Japan

Hp, Horsepower (Electrical) - The electrical horsepower is used by the electrical industry for electric motors and is defined to be exactly 746 W (at 100% efficiency).

Hp, Horsepower (Mechanical) - The most-common definition of horsepower for engines is the one originally proposed by James Watt in 1782. Under this system, one horsepower is defined as: 1 hp = 33,000 ft·lbf··min−1 = exactly 0.74569987158227022 kW or commonly 746 Watts.

Hp, Horsepower (Metric) - Metric horsepower, is defined as 0.73549875 kW, or roughly 98.6% of mechanical horsepower, or commonly 736 Watts. Metric horsepower began in Germany in the 19th century and became popular across Europe and Asia. The various units used to indicate this definition ("PS", "CV", "pk", and "ch") all translate to "horse power" in English, so it is common to see these values referred to as "horsepower" or "hp" in the press releases or media coverage of the German, French, Italian, and Japanese automobile companies.

Hp - Gauge mark denoting Horsepower, equivalent to 746 Watts (US) or 736 Watts (Europe, Japan) depending on the country that manufactured the slide rules.

HP35 - The electronic scientific calculator with an 8-digit  light-emitting diode display that was invented by Hewlett Packard in the mid 1972 which is credited with the sudden demise of  the slide rule industry.

Hughes-Owens - A Canadian based company distributing primarily Japanese Sun Hemmi bamboo slide rules under the H-O brand, as early as 1912. Additional models of H-O metal slide rules were supplied by US manufacturer Pickett in 1952. In the late 60's the same model numbers appeared on slide rules with a Geotec logo. A 1914 catalog shows Hughes-Owens importing Hemmi slide rules from 1912.

Hydralculator - Made by Lewis & Tylor Ltd., Gripoly Mills, Cardiff, the manufacturers of "underwriter" super fire fighting hose, for the use of their "Friends in the Fire Service." patent number 396,533 To find the quantity of water discharged for any given nozzle and a known pressure, place press on scale "b" opposite nozzle on scale "a', and read discharge through window in slide. To find height of jet for given pressure and nozzle diameter, proceed as above and read opposite arrow in center of slide, the height given on scale "d" for the appropriate nozzle.

Hyperbolic  - These Vector functions, Sh, Th are found on slide rules primarily geared toward electrical engineering, but have other uses such as defining the shape of a catenary curve.

Hyperbolog - A model of slide rule (ex: Aristo 0971) that has Hyperbolic and Log-Log scales.

Hyperlog - An Aristo 0972 Hyperlog is considered to be the most developed Aristo slide rule.




Index - The mark opposite the primary number 1 on the C and D scale is called the Index of the scale. The C and D scale have two indices, one at the left and one at the right.

Indicator - Another term for Runner or Cursor.

Industrial Revolution - The period in the late 18th and early 19th centuries when major changes in agriculture, manufacturing, production, and transportation had a profound effect on the socioeconomic and cultural conditions in Britain. The changes subsequently spread throughout Europe, North America, and eventually the world. The onset of the Industrial Revolution marked a major turning point in human society; almost every aspect of daily life was eventually influenced in some way.The slide rule's importance to the Industrial Revolution, and the impact of the Industrial Revolution upon the slide rule, are demonstrated by the proliferation of designs. From 1625 to 1800, the first 175 years after its invention, a total of 40 slide rule types, including circular and spiral designs, are recorded. The next 100 years, from 1800 to 1899, sees the creation of 250 slide rule types and manufacturers. Over 90 designs are recorded in the first 10 years of the 20th Century. ref: Oughtred Society.

Integer - A whole number without any fractional component. Called Prime Numbers when used for labeling the scale divisions.

Interpolation - Determining the approximate value of the location of the hairlines when positioned between two tick marks on a scale.

ISd scale - α/sin-1α), Inverted Sine differential scale, for sine range 0° to 90°. (PIC/Thornton) 

ITd scale - (α/tan-1α), Inverted Tangent differential scale, for tangent range 0° to 60°. (PIC/Thornton) 

Ivorine - Dennert and Pape (Aristo) brand name for the white celluloid plastic they introduced in 1886 to laminate wood slide rules as a better material than wood for the inscription of scales. This allowed a much improved precision and legibility to be achieved. Other manufacturers soon followed suit. 

IWA - IWA/F.Reihle GmbH & Co., a German family operated firm, Ingenieurerbüro für Wirtschafliches Arbeiten (Engineer's Office for Efficiency). Slide rules marked IWA began appearing in 1920 and in 1926, Frank Riehle, established a permanent company in Denkendorf, Germany. Product lines focused on special purpose plastic slide rules for mechanical engineers and under contract by other firms as marketing tools. Data slide rule" are still being produced for specialized purposes.




Jakar - A brand of slide rules sold in Great Britain, manufactured by the OEM Japanese companies Fuji and Hope.

Japanese Slide Rule Brands - Slide rules manufactured or re-branded by Japanese companies were Jiro Hemmi, Sans-Sai group, Relay, Ricoh, (US brands of Relay-Ricoh not listed), Giken, Fuji, Engineers, Hope, Kutsawa, Concise, (list incomplete).

Japanese Slide Rule Education - While the slide rule was a valuable calculating tool, a great proliferation of slide rules in Japan was the introduction of the slide rule into the curricula of senior and even junior high schools. When students started the school year, they were made to purchase a slide rule. The slide rule most commonly purchased by high school students in Japan was the Hemmi 2664S, a 25-cm simplex rule that appears very often in online Japanese auctions. The model was also touted as the ideal model to use in taking slide rule skill certification examinations, which were given in Japan until 1982, long after handheld calculator drove the slide rule out of the market as a viable product. At the height of the slide rule era in Japan, the fervor for slide rule learning (and teaching) was so great that the state-run broadcasting company even had a program devoted to the slide rule. Ref: William Lise.

Japanese Slide Rule Skill Certification - An elaborate system of slide rule skill certifcation examinations was developed in Japan, much of it through the efforts of Hemmi, having an interest in promoting slide rule use. The examination system continued until 1982, long after the electronic calculator had destroyed the slide rule as a commercial product. Two organizations held skill certification examinations: the Chamber of Commerce and the Association of Industrial High School Principals. Doing well in the examinations and the value of getting certified, with ceromonies at which awards were given, were even attended by Imperial family members, were a sure mark of acceptance of the slide rule into Japanese society. Ref: William Lise.

Jason - American brand of slide rule manufactured by Relay/Ricoh out of Japan.

J.C Penny Company - American catalogue company that sold slide rules manufactured by Relay/Ricoh out of Japan.

Jeppeson - American manufacturer, located in Denver, Colorado, of aviation charts and pilot supplies, including a version of the E6B flight computer slide rule, called the Slide-Graphics Computer.

Joe Miner - The official mascot of the University of Missouri-Rolla (UMR), which is now the Missouri Institute of Science and Technology , depicting a hard rock miner, packing a 6-gun and carrying a pick axe and a slide rule. Rugged and individualistic, Joe Miner personifies the spirit of the old west and the determination to succeed. His character is closely tied with the school's founding in 1870 as the University of Missouri School of Mines and Metallurgy.

Joint Rules - A hinged rule, typically pivoting in the center, such as the < a href="#Sector">Sector. These first (according to Peter Hopp) appeared around 1537.

Jones, Paul Jr. - (1896-1945) Born in St. Louis, MO. At age 42 was associated with the Waggener & Bros Lumber Company located at 318 West Main St,  Festus, MO.  which had recently acquired machinery for making window sashes, Jones used the machines to make a simple slide rule, using paper scales applied to the wood stock, and then started producing painted and printed scales, using the name Festus Manufacturing Company (1938), using the Waggener Bros facilities. He hired an east coast agent, (Magnus) M. Manheim Co. who had sales offices at 15 East 26th St, NY City to market slide rules under the name Acu-Rule Mfg Co to companies like Frederick Post, Dietzgen and D. Van Nostrand. With obvious success, the operation was moved to Jones' home town of St. Louis, MO in 1940 and incorporated as Acu-Rule Mfg. Co. Inc. Katherine Drew Jones, his wife, was listed as secretary and treasurer of the company in 1944. Jones wrote the instruction manuals, and as he expanded the line to include trig scales, he acquired the services of Professor Ross Middlemiss of Washington University in St. Louis, MO, to edit his work. The new office was located close by the W.U. campus, and it is entirely possible that Jones may have been a previous student of W.U., which precipitated his interest in mathematical instruments. Jones maintained leadership of Acu-rule until his untimely death in 1945 at the age of 49. Wilfred J. Boos became the new president and continued to expand the business with new designs. Katherine Jones was vice-president and secretary at least until 1947.




K scale - x3 , cube of D. Used for cubes or cube roots along with the D scale

K&E - Keuffel & Esser Co.

K&E Log Log Duplex Decitrig - The K&E 4081-3, according to a 1954 K&E catalog, was their most popular model. As with other K&E slide rules, the body was made of seasoned mahogany and the bonded laminated faces were a specially formulated plastic, its graduations individually engine divided for reliable precision to three decimal places by interpolation. Model numbers changed to N9081 and more modern versions, like the 68-1200, were made entirely out of plastic. Pocket versions were designated 4181-1.

Keikico - Japanese OEM manufacturer of slide rules for Relay, Ricoh, Sans & Streiffe, Lafayette, etc.

Kerby & Bro,Makers - Manufacturer of custom wood measuring devices. 1860 New York City directory showed them at 51 Fulton St., N.Y.. They made Rope Gages, Shrink rules, Tailor rules and custom slide rules for Forrest M. Towl. Owners were Daniel & Joseph Kerby, Kerby & Brother 50 Fulton St; The Trow New York Directory March 1890. Later the firm consisted of Robert D. & Joseph J. Kerby, Kerby & Brother 51 Fulton St; in the Trow New York Directory March 1909.

KERCS - Acronym for K&E Rotting Cursor Syndrome. Pre WWII K&E cursor mounts used a type of celluloid plastic that reacted to the tanning in the leather holsters, or sleeves, and after a time became very brittle. Many great K&E and Dietzgen slide rules have become unusable and worthless when struck by this disease, the bane of all slide rule collectors.

Keuffel, Wilhelm Johann Diedrich - (1838-1908). Inventor, entrepreneur and holder of many U.S. Patents dealing with slide rules. Born at Walbeck in Thuringen, Germany. Originally employed in the hardware business in Germany and Birmingham, England he emigrated to Hoboken, NJ in 1866. Keuffel joined with Herman Esser to become partners in the firm of Keuffel & Esser in July 1867 and sold imported drafting equipment. Wilhelm bought out Esser in 1902. Wilhelm died in Hoboken, New Jersey in 1908, the same year as Hermann Esser.

Kern & Co. Aarau Suisse - A Swiss manufacturer of surveying instruments, founded by Jakob Kern, located in in Aarau, Switzerland that provided products from 1819-1990, including specialized slide rules. See Kern & Co. History

Keuffel & Esser Co. - K&E Hoboken, New Jersey, , sold and manufactured slide rules, drawing instruments and other technical supplies. Founded in 1867 at 79 Nassau Street in New York by Wilhelm Keuffel and Hermann Esser. This was the first firm to exclusively carry drafting and surveying supplies. In 1875 the company moved to Hoboken, N.J. K&E was incorporated in February 1889. K&E sold imported slide rules from 1880, and began manufacturing their own rules in 1891. After a fire destroyed their building, a new facility was built in 1892-93 at 127 Fulton Street, Manhattan, NY. Hermann Esser's interest in K&E was bought out in 1902 by the Keuffel family. K&E continued manufacturing slide rules until 1976. Over the course of their history Keuffel & Esser became the largest manufacturer of slide rules and surveying equipment in the US and moved into CAD equipment in the 1980's. More about K&E history ( pdf) and K&E slide rules (McCoy's Catalogs).

Kiln-Dried - A process of drying hardwood, like mahogany, and other woods in an oven-like structure. The wood was used in early (circa 1930) slide rules made by Acu-Rule and others.

King, Otis Carter Formby - (1876-?) Born in Hammersmith, London, was the inventor of the Otis-King Calculator, a unique cylindrical Slide Rule with helical scales. By age 25 he was an electrical engineer and by age 46, he obtained two patents, British Patent 183,723 (Aug 3, 1922) and US patent 1,645,009 (Oct 11, 1923). The Otis-King Calculator was manufactured by Carbic Limited, London, England. Geneology from Susan Richards.

Klawun, Joe F. - ( ? - 1978) Founder of the Feinmessisnstitut (Precision Measurement Institute) Joe F. Klawun was opened in 1924 in Berlin-Charlottenburg, and after WWII moved its headquarters to Hanover in 1946. After the death of J.F. Klawun in 1978, sales continued under the direction of CENTRIC (Freise Werner KG).They built their own slide rules, but also distributed other german slide rules (Nestler and Faber-Castell). J.F. Klawun has sought particularly to the distribution of slide rules and offered to schools while the German manufacturers of related models, most of which were marked with fine measuring JF Klawun Institute. The model No. 1001/s was der Rechenstab fur Kaufmanns (The merchants' slide rule), as the Sterling monetary conversion scales imply. Their motto: "Alles was Rechnen erleichtert liefert Klawun": "Klawun delivers everything that makes calculation easier."

Koh-I-Noor Hardtmuth - A Czech manufacturer and one of the world's largest producers and distributors of a full line of pencils, pens, and art supplies. Formed in 1790 by Joseph Hardtmuth of Austria, the company was named after the Koh-i-Noor, a famous Indian diamond. In 1802, they patented the first pencil lead made from a combination of clay and graphite. Koh-i-Noor Hardtmuth eventually became a state-owned company after the Second World War, before once again becoming privately held in 1992 and being bought-out in 1994 by the Gama Group. Prior to 1978 they were a reseller of slide rules made by Graphoplex are also a contract manufacturer of small injection-molded plastic products.

Koh-I-Noor Slide Rules Fabrik Pvt. Ltd - Koh-I-Noor Slide Rules Fabrik Pvt. Ltd in India, (the relationship with Koh-I-Noor Hardtmuth is unknown), is still making special purpose plastic slide rules, including circular computers for aviation.They say on their web site: "We are the pioneer manufacturers of Slide Rules in India! In the year 1949, our company started the production of Slide Rules in 6" & 12" sizes for students, professionals and Army."

Konshak, Michael V. - (1947- ) Curator of International Slide Rule Museum, Vietnam Combat Veteran. Received Mechanical Engineering Technology degrees from Pikes Peak Community College (1978) and Colorado State University, Pueblo, CO. (1981). Was employed by Ampex, Digital, Control Data, Phillips, LMS/OSI. Optotech, Mountain Optec, StorageTek and Sun Microsystems. Career focused on optical and magnetic disk drives and arrays. 29 US patents issued, 10 Pending. Said to be a modern renaissance man with proficiencies in motorcycle racing, art, guitar, music composition, robotic combat, sky diving, aviation, solar electric homes, screenplays, writer, autocross racing, high powered rocketry and as a slide rule historian. Professionally retired.Portrait Collage

Korolev, Sergei - Sergei Pavlovich Korolev (1907-1966) is widely regarded as the founder of the Soviet space program. Involved in pre-World War II studies of rocketry in the USSR, Korolev, like many of his colleagues, went through Stalin's prisons and later participated in the search for rocket technology in occupied Germany. His incredible energy, intelligence, belief in the prospects of rocket technology, managerial abilities and almost mythical skills in decision-making made him the head of the first Soviet rocket development center, known today as RKK Energia. He deserves the most credits for turning rocket weapons into an instrument of space exploration and making the Soviet Union the world's first space-faring nation. His favorite slide rule was the Nestler model 23. Portrait Slide rule 

Kring - See Dutch Circle of Slide Rule Collectors (Kring).

Kruuse and Larsen Instrumentfabrik - Sarted by Kal Kruuse and Poel Larsen, two Danish partners who started out in a small garge in Valby on September 21, 1941, then partnered with DIWA to make slide rules. They had invented a logarithmic dividing (engraving) machine which made scales on wood stocks which was of interest to DIWA. Kruuse and Larsen were subsequently employed, along with their machine(s) to manufacture slide rules. Over the years the techniques and machines improved. During WWII sources for mahogony was obtained by buying used furniture and celluloid material was found in shoe repair shops During the 1950's 90 people were employed in the DIWA factory where Kruuse acted as production manager. After a 16 year relationship, they left DIWA in 1957 to start their own slide rule business , UTO. They stuggled with competing with post war Aristo and entered into economic distress in the 1970's along with other slide rule firms. UTO Poel Larsen and Kal Kruuse

Kutsuwa - Japanese manufacturer of inexpensive commodity slide rules out of plastic.

kW or KW hairline - Found on some slide rules with multi-lined cursors as a conversion factor. This is used with the PS (German notation for horsepower) hairline in conjunction with the C or D scale to convert kilowatts to British horsepower (and BHP to KW). 1 PS = .736 KW. Germany, England and China use 1 HP = 736 Watts. The United States, Japan and France use 1 HP = 748 Watts. Put the rightmost hairline at the right index of C and read the value under the center hairline to see which conversion factor is being used.

KZ scale - Found on a commerce slide rule where the CF and DF scales are folded at 360 (or 1/360) instead of at 3.14, and is used for determining compound interest over time.




L - Gauge mark conversion of Loge to Log10

L scale - log10x, used to determine the common logarithm or log (base 10), of a number on the D scale. Mantissa of the common logarithm of D.

L scale (electrical) - Inductive value in Henrys [Pickett N16-ES Electronic slide rule].

L or £ scale - See British pound (£) scale.

Laboratory Specialties Inc. - A distributor of "Slide Rules For Mathematics and Science Classes" located at 144 South Wabash Street, Wabash, Indiana. They sold what appears to be Acu-Rule Slide Rules Rules (models 10-J, 10-D, 50, 100), The Gilson Binary Circular Slide Rule and the Manual from WINSCO publishing. A K&E internal memo from A.W. Keufell in Feb 9, 1940 was passing around a Sales Flyer they obtained from this company probably to use for competitive analysis.

Lafayette - Lafayette Radio Corp.; New York, N.Y., 100 Sixth Avenue (Syosset). Formerly: Wholesale Radio Service Co. Inc.Trade names LaFayette, Trutest.The company sold radio sets, amateur radio equipment, citizen's band (CB) radios, and other communications equipment, as well as electronic components and even tools, through retail outlets as well as by mail-order. Lafayette was an early competitor to Radio Shack and Allied electronics. While Allied sold Pickett and Dietzgen rules, Lafayette sold re-badged Relay/Ricohs. This is probably the most common brand in the U.S., not only because they sold at least 5 different models, but did so for many years. Early rules often have "Lafayette" cases with "Relay" rules inside, and Known date codes span from 1958 to 1972.

Lambda or λ - Wave length of any propagated signal in meters, calibrated on basis of velocity of light [Pickett N16-ES Electronic slide rule].

Laminated - As in Laminated Bamboo or Mahogany. The process of applying a thin sheet of celluloid material onto one or more surfaces of a wood stock and slide of a slide rule which began around 1900. This was a major quality improvement in the manufacture of slide rules. The engine-divided marks cut into the lamination, then inked, provides a better contrast and readability for the user and extends the life of the slide rule. Some early laminations were 'pinned' with small nails or rivets to help adhere the ends to the wood or bamboo. Over time some laminations have shrunk at a different rate than the adjacent stocks, creating differing lengths of adjacent scales (Unique and Thornton).

Lampblack - Used as a pigment to fill in the divisions and markings on early of boxwood slide rules. Also known as Soot, Carbon Black and Lamp Black. is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon, that accumulates in chimneys, automobile mufflers, insides of smoke saunas and other surfaces exposed to smoke, especially from the combustion of carbon-rich organic fuels in the lack of sufficient oxygen. Lampblack is sometimes used only to refer to carbon deposited from incomplete burning of liquid hydrocarbons.

Lawrence Engineering Service - An American slide rule manufacturer, founded by George L. Lawrence, based in Wabash, Indiana (1935-38), later relocated to Peru, Indiana. A small 10 man shop, run by Ed Snyder, produced entry-level low-quality painted dime-store wood (basswood) slide rules. Highly under rated by most collectors, but they are probably responsible for putting more slide rules in the hands of pre-1945 students and non-technical people than any other brand. Lawrence was an OEM supplier to Post (model 1446D) during WWII, when Japanese importation was halted. George was divorced in 1947 and in the settlement gave the company to his wife Vivian which became Engineering Instruments (1947). Many specialty slide rules for farmers, electricians, photographers and plumbers, can be found that were made by Lawrence for other companies. Pure Americana.

LC scale - Used to calculate the resonant frequency (F) of an electrical circuit. If a circuit contains both inductance (L) and capacitance (C) it will resonate a particular frequency given by the equation: F = 1/(2π√(LC)). Found on the K&E Cooke Radio slide rules and in various forms on other models like the Pickett N-515, N-16-ES, and Hemmi 256. Electronic Slide Rules

Left-Handed Slide Rule - Left handed engineers may have been at some disadvantage with some models of slide rules, as well as Arabic speaking peoples who read from right-to-left. One instance of a slide rule that had the scales reversed was made by the British company Blundell in the 1970's.

Lehmann, Helmar - (Leipzig 1911) Studied Mathematics and Geophysics at Leipzig University. He worked for some time as a meteorologist and in 1946 became a teacher of Mathematics and Physics at various institutions including the Karl Marx University. In 1966 he published "Der Rechenstab und seine Verwendung" on the use of slide rules.

Lenoir - Late 19th century (c1820 - 1832) French slide rule manufacturer, Address: Rue Mayet 19, Paris, France. Began as the father and son firm of Lenoir in Paris as skillful manufacturers of slide rules. Lenoir, then prominent in France for its excellent astronomical and geodetic instruments, gradually advanced until, for a time, it held the very first place in the world in the manufacture of slide rules. The most common Lenoir slide rule, before the Mannheim, was the Soho. The father outlived his son and died in 1832. The Lenoirs were succeeded by Collardeau and Gravet. According to Maurice d.Ocagne, the name of the firm was first Gravet-Lenoir, then Tavernier-Gravet. (Reference History of The Logarithmic Slide Rule by Cajori).

Lerebours, Noel-Jean - (1761-1840) Paris. French manufacturer of Brass sectors, The first of the great opticians who helped make the French optical industry competitive with the English between the late eighteenth century and the 1820s. Spyglasses are an example. He began his career as a mathematical-instrument maker, but soon became famous for the perfection of his lenses. He also managed to produce better achromatic lenses than the English. After 1800, he was optician to the French Navy and the Bureau des Longitudes, as well as supplier to the Imperial family. He increasingly specialized in the production of large objectives.from Museum Galileo

Lietz Co. - The A. Lietz Company, San Francisco. Founded by German immigrant Adolph Lietz. The A. Lietz Co. was an American manufacturer of Engineering, Surveying, Mining and Nautical Instruments Instruments. The firm incorporated in 1892 under the name "The A. Lietz Company". Based in San Francisco, California, their building burned down in the 1906 earthquake and was rebuilt. In 1910 a complete line of drafting materials, including slide rules, and engineering equipment was added. They rebranded slide rules made in the United States, Germany, England and Japan, the models changing during the pre and post WWII era. In 1947, after 65 years of production, the firm discontinued the manufacturing of surveying instruments and begins to market Sokkisha instruments, made in Tokyo. Their business changed to being an importer and distributor. The Frank Paxton Company purchased the business in 1965 and moved its headquarters to Kansas City, Missouri. The company name was changed to "The Lietz Company." In 1980, Sokkisha acquires Lietz and establishes divisions in Australia and Europe. The Lietz distribution center moves to Overland Park, KS. In 1990 Sokkisha celebrates 70th anniversary and changes its name to SOKKIA. Lietz sold re-branded slide rules manufactured by foreign companies Relay/Ricoh, Concise, Sun Hemmi (Japan) and Faber-Castell (Germany) as well as American compaines like Gilson, Lawrence and Pickett. It is not known, at this point, when slide rules dissapeared from their catalogs.

Lietz, Adolph - (1860-1935 )Adolph Lietz was born in Leubeck, Germany in 1860. He immigrated to San Francisco in 1879 and worked in several scientific instrument shops before opening his own business. Lietz purchased the business of Carl Rahsskopff in 1880 and began his own business in 1882. Lietz originally joint ventured with another maker, Gottlieb A. Mauerhan, to form "Lietz and Mauerhan," a relationship that lasted for about a year. Following Mauerhan's departure, Lietz paired up with Conrad J. Weinmann who had previously worked for Carl Rahsskopff. The company was renamed A. Lietz & Co. and at that time produced surveying instruments and related tools.

Linear Scales - Non-logarithmic scales (technologists NEVER call them rulers) used to measure distance, typically marked in centimeters or inches. Sometimes scaled (2:1, 24:1, etc.) for drawing purposes.

Lightning Bolt symbol - A gauge mark found on the Deeva (India) Model 710 Tecknilog located on the CF scale at 3.29. Purpose unknown. A typical gauge mark 1/π = M is used for the conductivity of copper on electrical rules, but would be located at 0.3183.

LL scales - Log-log scales calculate X^Y using the C scale. Unlike the multiplication scales, the log-log scales do not require the user to determine the decimal point. The scales represent a  large range of numbers typically from 0.000045 to 22,000. Find Y on the C scale and read the result on the same LL scale. Powers of e are also directly read on the LL scales by setting the cursor to the power desired on the D scale.

LL or Ln scale - ln, "Lower" log-log scale, numbered 0 to 2.3, Logarithms (base e).

LL0 scale - e0.001x, Exponent of x.10-3 , numbered .999 to .99, Raising to a power x>1.

LL1 or ZZ1 scale - e0.01x, Exponent of x.10-2, numbered 1.01 to 1.12, Raising to a power x>1.

LL1' scale - The shortest known scale (10 divisions) on a slide rule found only on Relay/Ricoh like the Lafayette F-686 or Relay/Ricoh 157 Electronic slide rules. The following is all excerpted from the 1959 RELAY DUPLEX SLIDE RULES instruction manual. "...used with C and D scales. This LL'1 scale is [designed] by us to substitute LL1 and LL0 scales... ...As a extension of the C scale there is a very short scale at the right end of the C scale marked from 1 to 1.1 in red. This minute scale called LL'1 is invented in our laboratory to substitute the several lower LL scales in calculation of ln x, x to the y power, and e to the x power, etc. "

LL2 or ZZ2 or E1 scale - e0.1x, Exponent of x.10-1, numbered 1.1 to 3.0, Raising to a power x>1.

LL3 or ZZ3 or E2 scale - ex, Exponent of x., numbered 2.6 to 105, Raising to a power x>1.

LL00 or LL/0 scale - e-0.001x, Exponent of -x.10-3 , numbered .999 to .989, Raising to a power x<1.

LL01 or LL/1 scale - e-0.01x, Exponent of -x.10-2, numbered .99 to .90, Raising to a power x<1.

LL02 or LL/2 scale - e-0.1x, Exponent of -x.10-1, numbered .91 to .35, Raising to a power x<1.

LL03 or LL/3 scale - e-x, Exponent of -x., numbered .4 to 10-5, Raising to a power x<1.

Lionel-Porter - A merger of Lionel Corp. of New York, and the Porter Chemical Co. Hagerstown, Maryland. Both firms produced Scientific and Educational kits like the Lionel Inventor Series, Electronics and Plastics Engineering sets, Weather Station, Chemcraft (which came with a microscope), Microcraft, Biocraft, Labcraft, Mathcraft,Toolcraft, Mineralogy, 3-D Stereo-Vision, Geology, and Physical Science. Focused on ages 10 to adult, both boys and girls. The 1961 Mathcraft Expiremental Lab for $7.00, came with an Engineering Instruments 10-B slide rule, a 13 digit 1x4 Soraban (Japanese Abacus), a Sterling 4 digit Dial-A-Matic Automatic Adding Machine, and drawing equipment which included a compass, ruler, protractor, and two triangles and a manual with problems to solve. The kits came in a hinged metal portfolio.

Lübker, P. - Founded Lübker & Co. in Dresden-Klotzsche, Germany in 1932. At first it was operated as a trading company, offering drawing instruments and slide rules as well as a correspondence school. Lübker produced a well-known, but low quality, Rietz (model 72/2) and Lübkernorm slide rule machined out of beechwood. In 1947 the firm went bankrupt and was taken over by one of its workers, Horst Meissner. See alsoVEB Mantissa

Lübker & Company - Founded by P. Lübker in 1932, located in Dresden-Klotzsche, Germany. See VEB Mantissa

Lockhart, George L. - Slide Rule Designer, Manufacturer. Founder of Slide Rule and Scale Engineering Company in Laporte, Indiana in 1930, and later New Carlisle, Indiana. SR&SE made custom slide wood slide rules, such as the Concrete Quantity Calculator, as well as a standard Mannheim with A-B-C-D-K & L scales. Rules were manufactured using magnolia wood, finished white with an Ethyl-Cellulose base, then printed. A transparent lacquer coating was then applied to protect the printing. In 1945 a facility was built in Mt. Olive, Illinois. On February 14, 1947 the biggest fire in Mt. Olive history destroyed part of the factory. Production resumed in remaining buildings. On April 14, 1950 the company was declared bankrupt. Nicholas Muschong, a Vice president of Acu-rule, filed to do business in Illinois, and may have acquired the assets and copyrights. Similar in design and construction to Lawrence Engineering Services and Festus (Later Acu-Rule) Manufacturing. Other calculator models advertised in a 1940 flyer were Concrete Block and Mortar, Brick and Hollow Tile, Lumber, and Galvanized Sheet Steel Weight.

Loga - Swiss brand of circular (Disks) and cylindrical (roller drum) slide rules made by the company Billeter, Daemen-Schmid (Zurich, Switzerland), later renamed Loga (short for logarithm). Julius Billeter (1828 - 1914) was the original founder. Most of the cylindrical type were made in the 1930's and occupied a niche in the banking industry, while other manufacturers were making linear slide rules. The company stopped production soon after WWII.

Logarex - A slide rule made in former Czechoslovakia, as part of the U.S.S.R.

Log Log scale - A rule with scales for raising numbers to powers. Scales usually started with LL as in LL0, LL1, LL2, etc.

Logarithm - The logarithm of a number is the exponent of 10 representing that number. Since 101=10 and 102=100, any number lying between 10 and 100 can be expressed as 10 to some exponent between 1 and 2. For example, 59.4=101.774 by use of the L scale (3 place precision) and 101.77379 by the use of a logarithm table (5 place precision).

Logarithms (Concept) - Slide rules are based on the concept of logarithms. If you multiply a number raised to two different powers, the result is equal to the same number raised to the sum of the powers. This suggests a way in which multiplication, difficult with complicated numbers, can be replaced by addition, much easier even with complicated numbers. By positioning two scales, one on the slide and one on the stock, in such a way that you are adding the distance of one scale to another, you are effectively adding the logarithms of these numbers and therefore multiplying them. Similarly, by positioning the scales to get the difference in distance between two numbers, you are effectively dividing them.

Logarithms (Calculating) - On the reverse side of most Mannheim and Darmstadt closed body slide rules, will be found an evenly divided scale. The graduations are the mantissa of the numbers on the C and D scales. To find the log of a number, set the left-hand C index to a number on scale D, and opposite the the index line on the back of the body will be found the mantissa of the number required. On more modern duplex rules the L scale may appear on the same surface as the C and D scales.

Logarithms, Invention of - The logarithm was invented by three people, independently of each other, between 1553 and 1614, German Augustine Monk Michael Stifel, Swiss astronomer and mathematician Joost Bürgi and Scottish Mathematician John Napier.

Long Scale Slide Rules - These designs, typically found on circular, tubular, and cylindrical slide rules use helical and spiral scales to obtain a very long length over a short distance, enabling more divisions and greater resolution of the scales.

Longitudal lines - Lines added to a slide rule scale, in parallel with the slide, so that, in combination with the divisions, a series of boxes are formed. Also called E-Lines, or Embellishment lines. Used to aid hand-engraving of the scales. This practice stopped being used about 1930.

Lr & Cr scale - On a Pickett N16-ES Electronic slide rule, for any frequency read at arrow on F scale, the values of resonant condenser and inductance are opposite each other on Cr and Lr scale.

LU scale - same as LL2 scale.

Lucite - A type of transparent plastic used as early as 1939 to make cursors (indicators) for slide rules. Acu-Rule, Festus Mfg, Lawrence Engineering used Lucite.




m' Gauge mark - 1/60, minutes to degrees. Value: 1.666*10-2.

m'' Gauge mark - 1/3600, seconds to degrees. Value: 2.7788*10-4.

M - Gauge mark denoting 100/π = 31.83 or  1/π =.3183

M or ρ° (Rho°) - Gauge mark same as Q' or δ' (delta'), denoting minutes in a radian 3437.74 = (180 x 60)/π

M scale - On a commerce scale this is used for a relative date denoting the month. Used for calculation number of days between dates.

MacInnes, John - Slide Rule Award (Scholastic Achievement) Named for John MacInnes (1925 -1983) who coached the Michigan Tech Huskies for 26 seasons. The award is given annually to the hockey player with the highest overall grade point average. The player must have been at Michigan Tech for at least one full year. More on John MacInnes.

Made in Occupied Japan - This label was briefly required after WWII from 1945 through April 25, 1952 on 50% of all exports, including rebranded Japanese OEM manufactured slide rules, like Sun Hemmi and Relay/Ricoh (Nikkei-Relay). The notation appears on U.S. Slide rules like Post and Charvoz-Roos, especially those made by Sun Hemmi. Though conquered, some considered this tag a needless remembrance to their pride. During and after the war, many owners of Japanese slide rules ground out the "Made In Japan" off the slide rules they had used for many years.

Made in Occupied Germany - This label was briefly placed on rebranded German OEM manufactured slide rules like Nestler, Dennert & Pape and Faber-Castell after WWII from 1945 through April 25, 1952. Magnesium - A non-ferrous light weight metal used by slide rule manufacturers for the body and slide. Magnesium is a very chemically active element and significant oxidation occurs if left unattended. Today one often finds early Pickett or Acu-Math models with frozen center slides. A thin film of petroleum jelly (Vaseline) adds in prolonging the life of these slide rules.

Magnifier - A cursor or a removable lens that mounts over a cursor, that helps engineers with bad eyes, to improve the readability and interpolation of a slide rule with standard precision.

Magnolia - The wood used by the Slide Rule & Scale Engineering Co. in Illinois for the body and slide. Magnolia grows in the Southern states of the US, ranging into eastern Texas. Description: Fine textured, Moderately dense. Excellent machining qualities; turns very smoothly. Heartwood pale to light brown, sometimes with a greenish cast, displaying occasional mineral spots. It is closely related to the wood we know as yellow poplar.

Mahogany - Honduras Mahogany, the wood used by many slide rule manufacturers, like the U.S. companies K&E (Keuffel & Esser), Dietzgen and Acu-Rule for the body and slide. As mahogony slide rules were a sign of quality, some models of Acu-Rule (No. 10-J and 10-D) were stained to look like mahogany. Found in Southern Mexico, Central America, Colombia and Venezuela into the Amazon basin to northern Bolivia and eastern Peru. Description: Usually moderately soft, but density varies with growing conditions. Good strength to weight ratio. Heartwood light reddish brown or amber brown, darkening quickly upon exposure; sapwood lighter in color. Very stable, durable and an excellent wood for marine uses. Unsurpassed working and finishing qualities.

Maniphase - A Dietzgen model name of slide rule, which is a Mannheim rule with a cube scale "K" and an inverted single reciprocal "CI" scale added to the slide.

Mannheim - A standard single-face slide rule made to Victor Mannheim's specifications (1850), having scales to solve problems in multiplication, division, squares, square roots, reciprocals, trigonometry and logarithms. An early closed body design and the most common, basically a long flat body with a captured moveable centerpiece or slide as well as a moveable window with hairlines, called a "cursor". The Mannheim has single logarithmic scales on the lower half of the body and slide called C and D, which are the primary scales. On the upper half are double length logarithmic scales called A and B. Scales of Sin, Tangent and equal length are on the opposite face of the slide, and may be read directly by index marks on the underside of the body in conjunction with the scales on the upper side of the rule. Other modifications and improvements were introduced by Dennert (1886), Cox (1897), Beghin (1899), Furle (1899), Schweth (1901), Rietz (1902), Walther from the Politechnic of Darmstadt (1936).

Mannheim, Victor Mayer Amédée - (French, 1831 - 1906). He was a 19 year old student when he proposed the application and labeling of A, B, C and D scales in 1850. which slide rules of that type were later called Mannheim in his honor. He later became a French army artillery officer. Victor Mannheim Biography

Mantissa - The decimal part of the logarithm of a number (L scale). The exponent of 10 representing a number is made up of two parts - the integral part or characteristic and the decimal part or mantissa. The decimal part can be read directly from the slide rule by the use of the D and L scales.

MANTISSA, VEB - A GDR run company in what was East Germany. See VEB MANTISSA

Manufacturing Process - The steps used in the fabrication of slide rules, to insure quality and economic volume production.

Marque Depose - (en francais) French for "registered trade mark" in English. See Trademarks.

Mast Scales (E & M) - These scales appeared on carpenter's rules, with a Gunters slide, until the 1930's.Cutting a square timber into an octagon was a difficult computation, whose theory involved algebra, and whose execution involved radicals. This was the first step in the very frequent operation of making a ship's mast, in which a square timber was transformed into a tapered cylinder. If x is the distance from the edge of the log to the point where the cut began, algebra gives 2(a - x) = v2 x, where the timber is d = 2a wide. From this, it follows that d/x = 2 + v2 = 3.4142. The corresponding distance from the middle is y = a - x, or d/y = 2(1 + v2) = 4.8284. To find the distances x and y, new scales were added similar to the 1/p scales in the preceding paragraph, but with ratios 1:3.4142 and 1:4.8284 instead. These were called, respectively, the E (edge) and M (middle) scales. They were abandoned because no one made masts any more, not because the average carpenter could do the calculation some other way. Ref: J. B. Calvert

Mathcraft Expiremental Lab - The Lionel-PorterMathcraft Expiremental Lab, which sold for $7.00 in 1961 through 1969, came with an Engineering Instruments 10-B slide rule, a 13 digit 1x4 Soraban (Japanese Abacus), a Sterling 4 digit Dial-A-Matic Automatic Adding Machine, and drawing equipment which included a compass, ruler, protractor, and two triangles and a manual with problems to solve. The kits came in a hinged metal portfolio.

Moso Bamboo - Primary substrate material in Hemmi Slide Rules. Cultivated in Miyazaki or Kagoshima in Kyushu is 15 to 20 meter tall, has a circumference of 45 cm at people height, and a pulp of 1 cm thickness. In principle, only the outer hard bark is used to make thin square timber, but as the bark tends to bend to the inside, it is used as plywood by sticking to pieces together.

MDS Ltd. - The Manufacturers & Distributors Syndicate Ltd, previously the Miscellaneous Disposals Syndicate Ltd, of 41 St James's Gardens, Holland Park, London, founded in 1920 under disposal contract with H M Government. MDS sold slide rules out of their catalog made by other British and German firms.

Medaillis d'or - French for Gold Medal. An early (1883) K&E branded slide rule, made by the French firm Taverier-Gravet was awarded a Medaillis d'or in 1878 and 1879.

Metric Converter - A type of slide rule having scales to easily calculate metric (SI) meter-kilogram-Liter units to imperial/US/European units.

Meissner, Horst - A worker in the Dresden, Germany company Lobker & Co.. Meissner took over the business after it went bankrupt in 1947. The company was renamed Meissner KG and in 1972 was nationalized by the East German Government and renamed VEB Mantissa.

Meissner KG, Precision Instrument Factory - Dresden-Klotzsche, Germany. See VEB Mantissa.

Metrification - The process of converting a company or an entire country to the metric (SI) system of units. The metric system of measurement was developed during the French Revolution and was first promoted in the U.S. by Thomas Jefferson. Its use was legalized in the U.S. in 1866. In 1902, proposed congressional legislation requiring the U.S. Government to use the metric system exclusively was defeated by a single vote. K&E, and Dietzgen and other US slide rule manufacturer's have been putting metric scales on their slide rules since 1900. In 2004, the USA is only one of three countries NOT using the metric system, (even though we were all taught it in school) and it was mandated by Congress. The other two countries holding out are Liberia and Myanmar. In 1996, President George W. Bush signed an amendment to The Metric Conversion Act of 1974 requiring the U.S. Government to only buy products designed in metric whenever possible.

Metric System - See SI (International System of Units) and Metrification

Mechanical Engineer (Fowler) - A pocket watch chronographic style slide rule calculator made by Fowler (Manchester, England) between 1900-1910. One face has a long-scale and short-scale logarithmic scale. The short scale could be used for rapid calculations or as a check that the correct sector of the long scale had been used. The other face has a short-scale and reciprocals, logs, square roots, sin, tan and sin-tan scales.

Micador - Australian company formed in 1952 by MIChael A DORtimer, a post war European migrant. Distributed of Micador branded slide rules, made by Aristo and Ecobra. Micador 60 was the same as an Aristo 903. Other models known were Micador 10, 35 and 50.

Microglide - A Dietzgen trademark for a slide rule (like the Dietzgen 1734) having a Teflon slide bearing on the cursor for smoother action.

Micronta - American brand of slide rule manufactured by the Japanese company Relay/Ricoh. The Micronta 150 was the same as a Relay 150. Known date codes span 1956 through 1962.

Midget - A 4 inch diameter circular slide rule where answers are obtained by the use of two indicators connected to the center of the rule. The midget has 8 scales on the front side of a white enameled aluminum disk with two hairline indicators. Sold under the Atlas, Gilson, Dietzgen and Pickett brands.

Middlemiss, Ross R. - (1903-2001) In 1946, Middlemiss was a Professor of Applied Mathematics at Washington University and edited the basic manuals for the Acu-Rule slide rule company. Born in Marysville, Kansas, He received his advanced training in mathematics at the University of Colorado and taught there until 1929. Professor Middlemiss taught at Washington University for the next forty years, During the period from 1936 through the 1950's, he authored several books including a widely popular calculus textbook which was used in Washington University College courses until the late 1970's. In 1966 he was presented with a Washington University Distinguished Faculty Award (given annually at the university's Founders' Day celebration). In 1969, he retired as Professor of Mathematics and was given the status of Professor Emeritus.

Mil-Radian - A unit of measure used by the military and found on ballistic slide rules. The mil-radian is defined a 1/1000th of a radian. There are 2 pi radians (6283 mil-radians) in a circle. Early in the 20th century, the Infantry adopted the system but defined the "Mil" as 6280 Mils in a circle. Shortly after that the Artillery decided to refine the system and divided a circle into 6400 mils. A true mil-radian is equal to 3.4377 Minutes Of Angle (MOA), the Infantry Mil is 3.439 MOA, and the Artillery version is 3.375 MOA. The difference between the two versions of the "mil" is about two percent. See MOA

Minute Of Angle (MOA) - The common unit of measure for sight adjustments of artillery and infantry snipers. There are 360 degrees in a circle and there are sixty minutes in each degree. If a minute of angle is extended to 100 yards it will be 1.047 inches high. In order to simplify things some manufactures refer to a minute of angle as 1 inch at 100 yards. See Mil-Radian

Mono-Rietz - A one sided System Rietz slide rule.

Movies with actors using Slide Rules - See the Historical Photos of People with Slide Rules Gallery
Flight of the Phoenix (1965 - Character says to model airplane engineer "It's people like you who will inherit this earth.")
Tuskegee Airmen (1995 - K&E Demonstration rule in pilots class)
Apollo 13 (1995 - Engineers use slide rules, Post 1447, to calculate the battery life of the capsule)
Dr. Strangelove (1964 - Peter sellers uses a circular slide rule to calculate the time people must spend underground after nuclear holocaust)
Titanic (1997 - ship's engineer uses a simple Mannheim rule, to determine the amount of water spilling over the bulkheads)
This Island Earth (1955 - Cal Meacham has a Post Versatrig)
Invitation (1951 - Ruth Roman fingers Van Johnson's slide rule)
I want You (1950 - Dana Andrews works figures with slide rule)
The First of The Few (1942 - Actor Playing R.J. Mitchell, Spitfire designer, actually shot down and killed 1943, Fuller and Simples SR's showm)
The Beast From 20,000 Fathoms (1953 - Prof. Tom Nesbit calculating results of nuclear test)
Rumored to be in October Sky and A Beautiful Mind Fantastic Voyage (1966 - Edmond O'Brien claculates how long they can stop a human heart)
Full Court Miracle (2003 - Disney Channel. Algebra teacher estimating time a generator woul dstay running on available fuel)
Time After Time (1979 - Thacher played by H.G. Wells, shots of laboratory)
Voyage to the bottom of the sea (1961 - Admiral Harriman Nelson makes computations)
30 Seconds over Tokyo (1944 - Bombadier figuring time to bomb drop)
Revenge of the Nerds III (1992 - Pledges trying to figure out a SR while another reads the manual)
Die Hard 2 (1990 - Airport manager runs around with E6-B)
The Giant Spider Invasion (1975 - Dr. Langer's lab has 7' Pickett Demo rule)
The Hindenburg (1975 - Actor George C. Scott uses circular SR)
K-19: The Widow Maker (2002 - Actor Harrison Ford as Sub Commander calculates a torpedo solution)
When Worlds Collide (1951 - slide rule used at an observatory in South Africa)
Sky Captain and the World of Tomorrow (2004 - Actor triangulates the source of radio transmission)
Sabrina (1954 - Humphery Bogart mentions "slide rule accountants")
The Cat From Outer Space (1978 - Dr. Wilson calculates amount of gold needed to repair space craft)
To be continued...

Multi-lined Cursor - A cursor with more than one hairline, offset and parallel to each other.  Many advanced slide rules, especially those dealing with electrical calculations may have several hairlines that assist the user in making common calculations needing preset conversion factors. These hairlines are sometimes labeled as HP, KW, d, q, PS, 360, π/4, etc. These are used to make conversions such as horsepower to kilowatt. Others may help in geometry, where by placing the main line on a diameter of a circle on the D scale, the corresponding area of the circle may be read on the A scale under the other hairline.

Multiplication (Calculating) - The index on the left hand of the slide is adjusted to coincide with the multiplicand on the rule, and opposite the multiplier on the slide will be read the product on the rule.



n' Gauge mark - sine of 1 minute. Value: 2.909*10-4.

n'' Gauge mark - sine of 1 second. Value: 4.848*10-6.

Nakamura, A. - Japanese maker of early slide rules, where Jiro Hemmi worked before starting his own company.

Napier, John - Lord John Napier (latinized Nepero), Baron of Merchiston (1550-1617), Edinburgh, Scotland. Published the logarithm in 1614, after 20 years of developing the tables, which made it possible to perform multiplications and divisions by addition and subtraction and was the foundation for all future slide rule designs. Ex: a*b = 10^(log(a)+log(b)) and a/b = 10^(log(a)-log(b)). Michael Stifel and Joost Burgi are also attributed to the invention of logarithms. Napier Biography

National Union Radio - A U.S. manufacturer in Newark, New Jersey, that designed an electronic slide rule which was made for them by K&E.

NASA - National Air And Space Administration - United States Astronauts used slide rules up until 1972.

Nestler, Albert - (1851-1901) Founded Beck & Nestler in 1879 with Theophil Beck. When Beck retired, the firm became just Nestler.

Nestler, Albert - (1877-1961) Technical Director of Nestler AG. Albert and his brother Richard Nestler were the sons of the founder Albert Nestler. After the death of Albert Nestler in 1901, By 1955, both sons had expanded the factory with 600 workplaces. Note: In this painting he is leaning at a dividing machine for slide rules).

Nestler, Jürgen - (1940- ) Great grandson of founder of Albert Nestler Co. in Lahr, Germany. Jürgen was a mangager in factories providing injection molds as a supplier for the automobile industry and was a member in the german VDI (Verein Deutscher Ingenieure, Society of German Engineers). His apprenticeship was in the Nestler factory and after his education, constructed constructed amny of the machines. A generous benefactor of the Oughtred Society, to which he donated 50 new Nestler slide rules for inclusion at no cost to buyers in the OS Slide Rule Learning Kit. Jürgen contributed the Nestler family portraits shown in this gallery along with other useful information including some personally owned slide rules. He donated a large collection of Nestler slide rules to several museums, including the Lahr Museum, in Lahr, Germany, the State Museum for Technology and Labor in Mannheim, Germany and the International Slide Rule Museum (ISRM), based in Colorado.

Nestler, Richard - (1878-1956) Commercial Director of Nestler. He and his brother, Albert, were the sons of the founder Albert Nestler.

Nestler AG, Albert - German slide rules company in Baden, Germany. In 1878 Albert Nestler founded Beck & Nestler with Theophil Beck. After Beck's retirement, the firm became just Nestler. They made drawing and surveyor instruments and started making slide rule in 1880 and becamethe biggest manufacturer of slide rules in the world by 1939, exporting to more than 60 countries.Their first slide rule was a Mannheim. In 1903 NESTLER marketed and sold under license first the System Rietz. It was made of celluloid veneer on mahogany. In the beginning the scales ran from 1 to 10, to 100, then later these scales were extended at the beginning and end of the scales resulting in extended reading and scope for adjustment. Their PRAEZISION model of 1912 had an extended root scale, folded at the square root of 10. This gave a 10" slide rule the precision of a 20". In 1962 their top-model MULTIMATH-DUPLEX, also featured this idea. For many years Nestler's slide rules used a mahogany wood base faced with PVC (called Anagit) laminated scales.The change from wood to full PVC (Astrolon) occured in 1952. Many of these plastic models were later supplied by the Japanese firm Uchida Yoko. They stopped manufacturing slide rules in 1972 and changed over to modern drawing and calculating equipment. The old stock of slide rules were destroyed or sold to third world countries as there was no other market, however many were retained by Nestler family members and later donated to museums.

Newton, Sir Isaac - (1642-1727), mathematician and physicist, one of the foremost scientific intellects of all time. Born at Woolsthorpe, near Grantham in Lincolnshire, where he attended school, he entered Cambridge University in 1661. In 1675, Newton designed an instrument for solving equations that consisted of two or more rulers that used a hair [line] to read off numbers across the scales. Refer to Newton's polynomial solver by Christopher J. Sangwin, 2002. This may have been the forerunner of the cursor but the design of a cursor directly attached to the slide rule is attributed to John Robertson.

Nickel-Silver - A type of electro-plated material used to coat the steel end plates of early K&E and other manufacturer's slide rules to minimize corrosion and add esthetic appeal to the product. Old slide rules stored for decades in their leather sleeves may come out with a 'greenish' powder coating coating the end plates which is easily cleaned off.

Nobema - NOBEMA Products Corporation. Pleasantville, NY (1921) and later New York 12 NY, Imported and rebranded artist and drafting supplies, circa 1950, several items being a re-branded Lawrence (US), Unique (Uk) and Aristo (Germany) slide rules. Nobema Products Corporation was established in 1901, but was bought by the founder of the Riebe's Artists' Materials in the 1930s.

Norton & Gregory, Ltd - A British supplier of slide rules and drafting equipment. A 1907 Roto-Rule Instruction sheet has an address of Castle Lane, London, S.W., England as well as in Glasgow. In 1958, Admel International, a supplier of Diazo materials, obtained control of Norton & Gregory, and in 1971 the company went into voluntary liquidation.

Novotni Slide Rule Co. - Novotni, located in Media, Pennsylvania, made special use slide rules, the most well know being their Weight Slide Rule for Blacksmiths and other manufacturing disciplines. Some of these were made out of black bakelite (c1925), suitable for use next to foundry, and later they were made of wood with a paper laminate or pasteboard. A 1959 version appears to have been made of white plastic.




Occupied Japan - many Japanese slide rules, specifically made by Sun Hemmi, were engraved with "Occupied Japan". Japan was occupied by the U.S. Armed Forces September 1945 and the treaty to un-occupy was September 1951, becoming effective April 1952. Anti-Japanese sentiment was still very high during this time and many post WWII imported Hemmi slide rules are found with any reference to Japan gouged out.

ODELCO - De Leon Import & Export Corporation, was founded in the Phillipines by Oscar de Leon in 1952 and began distributing the Hemmi line of slide rules, along with other products from the United States, Japan and Germany. ODELCO branded slide rules were intended for the Phillipine market, but many found their way to other parts of the world, possibly because of the large number of U.S. personnel assigned in the military installations in the Philippines that brought them home. Today, Odelco's president is Oscar de Leon, Jr, and continues to distribute GPS equipment, geodetic, geological, oceanographic and environmental equipment for engineers, laboratory and testing equipment, agriculture and veterinary instruments, vocational technology systems and office equipment in the Philippines. See their corporate site.

OEM - An Original Equipment Manufacturer which manufactures products for re-branding by other companies. Hemmi is an OEM to Post.  Relay and Faber-Castell are OEM's to Dietzgen, etc.

Hisashi Okura - (1892-1960) Founder of Hemmi Slide Rule Co., Ltd.(1933) was born in Kumamoto prefecture, in the south of Japan. Born in the Otsuka family, a family with a member in the government Cabinet during the Meiji era, he married the oldest daughter of the Okura family, owner of the then Okura brewing company (now Gekkeikan Sake) and became member of the family. In 1924, Hisashi had proudly found a Japanese Hemmi's slide rule in a shop in London when was traveling around the world. Jiro Hemmi had experienced some business setbacks because of a fire in his shop, and when Hisashi came to visit Jiro in 1925, he offered to help expand the business. He assisted Jiro Hemmi in managing his shop and actively promoted exportation to respond to demand from foreign countries. They formed a partnership in 1928. Hisashi directed the development of slide rules which could compete with the well-known ones from other countries. He also implemented a research department in which he committed to developing original Japanese slide rules.

O'Leary, Michael - (1951-2003) A modern day prolific and knowledgeable collector of slide rules, specializing in K&E's, who was well known and respected amongst slide rule groups throughout the world. If you collect slide rules, you will run across mentions of Michael O'Leary on many web sites and group meetings. Memorial

Olson - An American electronic radio parts supply and catalog company, founded by Olson brothers, Sidney, Irving and Philip, based in Akron, Ohio, that had a chain of franchise store throughout the United States. Olson also sold branded slide rules manufactured by Relay/Ricoh out of Japan. The Relay 150 was also labeled with the Olson model number of TL-373. Model TL-472 was used for electrical calculations. Most stores closed after 1985 possibly because personal computers were becoming more interesting than building radios.

Olson, Sidney - (1915-2000) One of the founders of Olson Electronics, a leading national CE chain in the 1950s and '60s, With his brothers Irving and Philip, Olson started a radio repair business in Akron, Ohio, in their father's garage in the early 1930s. The project evolved into the Olson Radio Warehouse in Cleveland during the late 1940s and then became Olson Electronics, a chain that had more than 80 retail locations coast to coast at its height. In 1968 the company was sold to Teledyne, and after a few years Olson and his wife Miriam retired to Miami Beach, where he began a life of philanthropy. Several years later he returned to run the operation, but in 1977, was permanantly retired.

Open-Body Slide Rule- A slide rule having a body or stock fashioned from four or more pieces that enable the user to see through the opening caused by the removal of the slide. Early wooden and high-end plastic open-body slide rules have end-peces or Braces joining the upper and lower body parts with metal plates and fasteners. Modern open-body plastic slide rules have molded braces that form the bridge. See Closed-Body Slide rule.

Open Loop - Conventional definition: In an electronic control circuit, a system that does not have constant feedback in order maintain the stability of a signal or motor, as would be in a closed-loop system. Mike's definition: Engineer 'speak' for someone who is out-of-control, reckless or irresponsible, wandering aimlessly, or without restraint. Teenagers. Slide rule collectors. Sometimes associated with engineers who want to keep changing their design (we can't help it!). Quote: "There comes a time in every project where you have to shoot the engineer and ship the product" (origin unknown).

omega or ω - Angular rotation frequency in radians per second [Pickett N16-ES Electronic slide rule].

Omega (Blundell) - A model series of slide rules for professionals manufactured by Blundell (BRL), and later Blundell-Harling (BHL). The Omega and Janus series were more expensive than the Academy series. The Omega 400 series, for instance, had a special, patented adjusting device for the tension and were supplied with a special screwdriver for its adjustment. Towards the end of general purpose slide rule production the Omega series were phased out.

Omega (Relay/Ricoh) - American brand of slide rule manufactured by Relay/Ricoh out of Japan.

Omnes Rule - An all-metal slide rule that came with two slides that could be swapped out to provide more useful scales to the user. At the time, it combined the best features of the Gravet, Fix, Rietz, Jackson Log-log, Faber, and C.E.M. Slide Rules.

Order(s) of Magnitude - An order of magnitude is an exponential change of plus-or-minus 1 in the value of a quantity or unit. The term is generally used in conjunction with power-of-10 and expressed as scientific notation in writing the calculation and result. In base 10, the most common numeration scheme worldwide, an increase of one order of magnitude is the same as multiplying a quantity by 10. An increase of two orders of magnitude is the equivalent of multiplying by 100, or 102. In general, an increase of n orders of magnitude is the equivalent of multiplying a quantity by 10n. Thus, 2315 is one order of magnitude larger than 231.5, which in turn is is one order of magnitude larger than 23.15. As values get smaller, a decrease of one order of magnitude is the same as multiplying a quantity by 0.1. A decrease of two orders of magnitude is the equivalent of multiplying by 0.01, or 10-2. In general, a decrease of n orders of magnitude is the equivalent of multiplying a quantity by 10-n. Thus, 23.15 is one order of magnitude smaller than 231.5, which in turn is one order of magnitude smaller than 2315. Scientists and engineers have designated prefix multipliers from septillionths (10-24) to septillions (1024), a span of 48 orders of magnitude. See SI (International System of Units).

Order of Magnitude Estimate - An order of magnitude estimate of a variable whose precise value is unknown is an estimate rounded to the nearest power of ten. For example, an order of magnitude estimate for a variable between about 3 billion and 30 billion (such as the human population of the Earth) is 10 billion. An order of magnitude estimate is sometimes also called a zeroth order approximation.

Otis King Patent Calculator - Made by Carbic Limited, 51, Holborn Viaduct, London, England. This pocket sized (when collapsed) cylindrical slide rule is named after its inventor, Otis Carter Formby King (1876-?) a grocer and electrical engineer. The metal slide rule design incorporates spiral (helical) scales having the equivalent scale length of 66 inches. Both Model K and Model L have an ingenious bearing mechanism which allows for smooth operation of the cylinders. With a log-scale decade length of 66 inches, the Otis King calculator should be about a full digit more accurate than a 6-inch pocket slide rule. But due to inaccuracies in tic-mark placement, some portions of its scales will read off by more than they should. For example, a reading of 4.630 might represent an answer of 4.632, or almost one part in 2000 error, when it should be accurate to one part in 6000 (66"/6000 = 0.011" estimated interpolation accuracy). Otis King Slide Rules were made from 1917 through 1972. British Patent 183,723 (Aug 3, 1922) and US patent 1,645,009 (Oct 11, 1923). Otis King's were rebranded for some U.S. Companies, Like Geniac. Manual - 8 page PDF and Types

Oughtred Society - The Oughtred Society is an international Slide Rule Collector Organization, founded in 1991 by a group of like-minded slide rule collectors, based in the United States. Goals of the organization include the dissemination and sharing of information about slide rules, encouragement for slide rule collectors and preservation of slide rules, their history and associated ephemera. The Journal of the Oughtred Society (JOS) is published twice a year for all members. Annual meetings are held on both coasts of the U.S.A. More

Oughtred, William - (British, 1574-1660) An ordained Anglican minister, is considered the true inventor of the slide rule by taking (1625) two Gunter's lines (scales) and sliding them relative to each other thus eliminating the dividers. The lines were used in both the linear (straight) and circular forms. In the former two scales were held against one another by the hands. The circular version replaced the dividers by including an "opening index" really a pair of dividers rotating on a hub at the center of the circular scale. He also introduced the "x" symbol for multiplication, as well as the abbreviations "sin" for sine and "cos" for cosine in his Clavis Mathematicae (1631), composed for instruction of his pupil, the son of the Earl of Arundel. Oughtred was born at Eton, and educated there and at King's College, Cambridge, of which he became fellow. Being admitted to holy orders, he left the university about 1603, and was presented to therectory of Aldbury, near Guildford in Surrey; and about 1628 he was appointed by the earl of Arundel to instruct his son in mathematics. He corresponded with some of the most eminent scholars of his time on mathematical subjects; and his house was generally full of pupils from all quarters. Oughtred published, among other mathematical works, Clavis Mathematicae (The Key to Mathematics), in 1631; a treatise on navigation entitled Circles of Proportion and the Horizontal Instrument, in 1632, which described the first slide rules and also sundials, works on trigonometry and dialling, and his Opuscula Mathematica, published posthumously in 1676. See Gunter, Edmund. Also Wingate, Edmund. William Oughtred Biography by John Aubrey c1650



p Gauge mark - (π/180) Radian to degrees conversion. Value: 1.745*10-2.

p' Gauge mark - 60*(π/180) Radian to degrees conversion. Value: 3.438*102.

p'' Gauge mark - 3600*(π/180) Radian to degrees conversion. Value: 2.063*105.

P scale - Reads sines of angles on Θ or RΘ. The Pythagorean scale, used in determining the base of a right triangle if the hypotenuse and height are known. You set D as the value height/hypotenuse and read the ratio base/hypotenuse on P directly.

P scale - 1/T, Reciprocal of T1.

P0/P1 scale - 1/T1, Commercial, reciprocal of T1.

P2 scale - 1/T2, Commercial, reciprocal of T2.

P0/P1 scale - 1/T1, Commercial, reciprocal of T1.

P1 scale - √(1-x²), 0.995 to 0.

P2 scale - √(1-x²), 0.99995 to 0.995

Palmers Computing Scale - An early early version of the first circular slide rule published in America (first issued in 1843). Palmer and the engraver George Smith began working on their design for an "endless computing scale" in early 1841. It was copyrighted in Boston in late 1843, and versions of the device continued to be produced until at least 1852. Palmer's slide rule enjoyed only a limited success, largely because of poor marketing and the American public's fear that use of the device "[would] tend to weaken the mind, by causing it to rely upon mere mechanism to make its numbered computations" (Fuller, Key to Fuller's Computing Telegraph [1846], quoted in Feazel 1994, 15). Palmer also published A key to the endless self-computing scale, showing its application to the different rules of arithmetic (Rochester: P.S. Stoddard, 1842). Ref:Origins of Cyberspace 353.

Pi or π or π-line (A and B scales) - Gauge mark denoting the constant π = 3.14159

Pi or π or π-line (D, or DF scales) - Gauge mark denoting the constant π = 3.14159, used for finding the perimeter of a circle (L=d²π/4) when the diameter is known. Using the hairline, Set the index of the C (or CF) scale on π of the D (or DF) scale. For any diameter on the C scale, read the perimeter on the D (or DF) scale.

π/4 - Gauge mark of π /4= 0.7854 - used to quickly find the area of a circle from it's diameter. The area of a circle A =πr²= (π/4)d² but in practice it is usually the diameter that is known. Normally you would go D / 2 x D / 2 x pi, or D x D / 4 x pi ( too many steps). This special mark enables you to just go D x D x 0.7854. The entire calculation can be done in one motion: Set 1 on 'C' opposite diameter on 'D', and read the answer on 'A' opposite 7854 on 'B'.

π/4 hairline - Found on some European multi-lined cursors as a conversion factor. The π/4 (or 0.7854) hairline is used in conjunction with the central hairline on the cursor and the A scale.

Pape, Martin - (1834-1884) Cofounder of the German firm Dennert & Pape (1862). After his death, Dennert still kept Pape in the company name until it was changed to Aristo.

Parallax Error - An discrepancy in reading a gauge, meter or slide rule when the hairline or indicator needle is not viewed directly above the instrument. In the case of a slide rule, Hairlines are generally placed on the bottom of the glass cursor as close to the stock as possible to minimize this effect.

Partridge, Seth - (1603-1686) A surveyor and mathematical writer from Hertfordshire, England. On 1 Aug. 1657 Partridge completed a mathematical work, entitled The Description and Use of an Instrument called the Double Scale of Proportion published 1671-72. In this work, Partridge described the use of three rulers, one of which would slide between the other two, held together by brass or wood at the ends. This slide rule had scales on both front and back faces and this layout was the first duplex rule, becoming a common type for more expensive rules into modern times.

Pascaline Mechanical Calculator - Designed in 1642 by Blaise Pascal (1623-1662). One of the world's first mechanical adding machines which used a series of toothed wheels, which were turned by hand and which could handle numbers up to 999,999.999. Pascal's device was also called the "numerical wheel calculator".

Patent - Patents protect the manufacturer or inventor of a design or construction methodology from being copied and exploited by others. Design patent, in the USA, cover the "look" of an invention. Utility patents cover the actual unique physical characteristics. The mention of a patent is normally followed by the unique patent number (for a particular country) that it was issued under. The earliest known slide rule patent in the USA was in 1851. The United Kingdom issued Letters of Patent as early as the 1630. (personal note:  Japan's patent system allows Japanese companies to 'steal' western patents and call them their own).

Patent Date - The date a patent was issued. Although marked on a slide rule, is not representative of the date of manufacture as the patent may have existed for over 30 years.

Patent Pending - Patents that have been applied for and not yet issued are considered pending. It lets other inventors/manufacturers know that a date has been established for the time of the original idea by its inventors. As of 2004, the US Patent and Trademark office is taking 4 years to issue patents that have been submitted.

Pearwood, Swiss - A wood used for the stock of early A.W. Faber, faber-Castell laminated slide rules. They also used Boxwood.

Penol Company - Penol (which stands for Pen Olsen) was founded in Denmark by Christian Olsen making writing instruments. Christian received the distribution rights for Parker in Denmark, Sweden and Norway in 1905. The Penol brand was established in 1928. In 1932 a factory was opened and licensed Parker together with Penol pens were produced. Plastic slide rules with the Penol brand were produced in the 1960's. Production of fountain pens stopped in 1966, but the Olsen Company still represents Parker and distributes Parker products in Scandinavia. Note: The great American scientist George Washingtion Carver also started the Carver Penol Company (1926) in the USA making a medicine made of peanut oil and a creosote emulsion.

Perspex - A transparent Acrylic plastic used to make slide charts. The name 'Perspex' is used in Europe, the US name being 'Lucite'.

Phase shift angle, Θ scale - Phase shift angle (voltage with respect to current) of circuits whose phase increases with decreasing frequency (reads against frequency on F scale) [Pickett N16-ES Electronic slide rule].

Phase shift angle, α scale - Phase shift angle (voltage with respect to current) of circuits whose phase increases with increasing frequency (reads against frequency on F scale) [Pickett N16-ES Electronic slide rule].

Phillips - A Dietzgen model, circa 1938, name for a single sided rule similar to a Polyphase but with an inverted A scale (typically labeled R) instead of an inverted C scale (CI) and an E scale, what other manufacturers call a K scale (cube scale), which is read against the C/D scales.

Photoetching - Photoetching, also known as chemical milling, is a process that removes metal using a chemical reaction and is useful in creating highly accurate features or cuts, in this case, scales on metal slide rules and the thin flat springs used in some cursors. Using a photographic mask to place an emulsion, or photo-resist, on the metal, ferric chloride, or some other corrosive is used to erode the unprotected surfaces. The length of the time that the parent material is immersed determines the depth.

Photo Slide Rule - A slide rule specifically oriented to photographers to aid in determining settings for flash lamps and focus. One example was manufactured by Acu-Rule for AREL Inc, St. Louis, MO.

P.I.C. - The Precision Instrument Company was a British slide rule manufacturer that was acquired by Alexander Thornton (Thornton A.G.) in 1900. The P.I.C. slide rules were made of mahogany and had framed-glass cursors and springy-stator floors. A 1930's Thornton catalog lists more than 70 models carrying the P.I.C. brand name.

Pi (π) - The number pi represented by the greek letter π, is a mathematical constant that is the ratio of a circle's circumference to its diameter. The constant is approximately equal to 3.14159265. It has been represented by the Greek letter "p" since the mid-18th century. p is an irrational number, which means that it cannot be expressed exactly as a ratio of two integers (such as 22/7 or other fractions that are commonly used to approximate p); consequently, its decimal representation never ends and never repeats. It is a transcendental number - a number that cannot be produced with a finite sequence of algebraic operations (sums, products, powers, and roots). The transcendence of p implies that it is impossible to solve the ancient challenge of squaring the circle with a compass and ruler. Observant visitors will notice that all slide rules, electronic 'slide rule' calculators and even abacuses are set to the number pi (up to the precision of the artifact0. This is the curator's favorite number.
π = 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679

Pickett - An American manufacturer of slide rules characterized by all metal construction. The founders, Roswell Colvert Pickett and Arthur F. Eckel started out making all-metal slide rules in 1944 using magnesium and later evolved to aluminum as aluminum alloys became more machinable. Pickett slide rules were chosen to be used by the Apollo astronauts on their mission to the moon, as they were lighter than their wood core counter parts. Picketts are remembered by many later-day alumni for their characteristic yellow 'eye saver' color. Pickett also produced all-plastic low-end slide rules in the waning days of the their life. When the company folded with the rest of the industry, the slide rules were going to be sold as scrap metal to Mexico, but were rescued by Dick Schwartzer and later sold to collectors over the last 25 years. There are thousands of the plastic Pickett models hiding in warehouses waiting to be slowly feed into the collector market. Expanded Pickett Timeline

Pickett, John Wickersham - (July 14, 1926 - ) Son of Roswell Colvert Pickett, co-founder of Pickett and Eckel Co. Born in Chicago, John worked in the marketing of P&E after receiving his MS in Business from the University of Southern California. He founded Pacific Leather Works to make leather sleeves for Pickett in 1953 and became president of Pickett & Eckel in 1957.

Pickett, Roswell (Ross) Colvert - (Mar 27, 1892 - Dec 23, 1969) Co-founder of Pickett and Eckel Company in Chicago, 1943. His background skills were as a printer, which he used to create printed scales on a cardboard model, then progressed quickly to all-metal bodied slide rules. His oldest son was Allen Roswell Pickett. His second son, John W. Pickett, later took over the reigns of the company. Ross was buried in Santa Barbara Cemetary, CA. (Geneology information found in Margo Louise Pickett's family Bible purchased at a garage sale in Chicago around 1980 by John Albert.)

Pickworth, Charles N. - c1900. Wrote the English versions of A.W. Faber's slide rule manuals. Newark, New Jersey, USA.

Piehl, R.J. - (?-?) President of Frederick Post Co. post WWII. Visited Sun Hemmi in Japan November, 1954 to discuss a plan for expanded business.

Plastic - A polymeric engineering material used to make slide rules. Celluloid was the first use of plastic as a coating or laminate over hardwood bodies and slides. Later acrylic plastic cursors began to replace glass. Celluloid was replaced by PVC (Polyvinyl Chloride - US Geon and German Astralon, Cobex and Darvic) and polycarbonates in rule construction. The Germans (Faber-Castell, Aristo, Nestler, etc.) were the first to popularize all plastic slide rules. K&E's had a trademark synthetic material called Xylonite, and later it became Ivorite after 1955. Mike's opinion: Although the last generation of slide rules are beautiful with many their varied colors, the warmth and feel of celluloid covered wood still feels better in my hand.

Plastograf - A Brazilian manufacturer of slide rules located in Sao Paulo, Brazil (Brasil).

Pocket Slide Rule - A short, pocket sized,  version of a slide rule with the scales compressed to fit on a body typically less than 12.5 cm (6 inches) long in length. Some models may be as short as 10 cm (4 inch). (Typical precision of a pocket slide rule is two (2) significant digits.

Pocket Watch - A slide rule in the shape of a pocket watch, invented by Sperry, manufactured by Fowler. A more modern version is the Russian (USSR) KL-1.

Polylog - A Diwa (Denmark) and Deeva (India) model slide rule having 25 scales.

Polymath - A Dietzgen model name of a duplex slide rule with trig scales, but no log scales.

Polyphase - A Mannheim with added scales for cubes and cube roots with an inverted C scale (CI). Some manufacturers used Mannheim and Polyphase interchangeably.

Position Line Slide Rule - A device for calculating a position within 1 minute of arc on earth for solving the celestial trinagle used for navigation, in conjunction with a sextant, particularly in WWII aircraft. These were cylindrical in nature with spiral scales and were first designed by Captain Leonard Charles Bygrave of the Royal Air Force (R.A.F.) in 1920, initiated by the Air Ministries Laboratory (A.M.L.) in Kensington, London. Conventional slide rules with tables could be used in ships, but the Position Line Slide Rule was much quicker to use when traveling fast as in aircraft. See the article on Position Line Slide Rules written by Ronald W.M. Riet in 2008.

Post - Frederick Post Co., Chicago, founded 1890, was a distributor of US brand slide rules, and other engineering supplies, which were typically relabeled standard products from well-known manufacturers from around the world. At one time or another Post brand slide rules were made by Dennert & Pape (became Aristo), Nestler, A.W. Faber (became Faber-Castell), Hemmi, Lawrence Engineering Service, Charvoz-Roos, Bruning and Gilson. Post also sold branded slide rules from Richardson, Vicari, Boucher, Sexton, Halden, Chandler, Ritow and Winslow. Richardson was a supplier to Post in 1912 and Post began importing Sun Hemmi slide rules with the Post brand around 1920. Until about 1932, some Post models were made by a variety of German manufacturers. During WWII, Charvoz-Roos and Lawrence supplied slide rules were branded with the Post name. Post was acquired by Teledyne in 1970. The Versalog 1460 made specifically for Post by Hemmi is their most well known and collected slide rule.

Pound (£) scale - Monetary scale. See British pound (£) scale and sh.d scale.

Precision (false) - A slide rule tends to moderate the fallacy of "false precision" and significance. The typical precision available to a user of a slide rule is about three places of accuracy. This is in good correspondence with most data available for input to engineering formulas (such as the strength of materials, accurate to two or£ three places of precision, with a great amount, typically 1.5 or greater, of safety factor as an additional multiplier for error, variations in construction skill, and variability of materials). When a modern pocket calculator is used, the precision may be displayed to seven to ten places of accuracy while in reality, the results can never be of greater precision than the input data available. A slide rule requires a continual estimation of the order of magnitude of the results. On a slide rule 1.5 X 30 (which equals 45) will show the same result as 1,500,000 X 0.03 (which equals 45,000). It is up to the engineer to continually determine the "reasonableness" of the results: something easily lost when a computer program or a calculator is used and numbers might be keyed in by a clerk not qualified to judge how reasonable those numbers might be. (ref:Wickipedia).

Precision (of a slide rule) - The precision of a slide is customarily based upon the number of divisions and sub-divisions of the scales that allow the user to interpolate the position of the interacting scales and cursor as well as to determine the corresponding result that is being sought. The measure of the precision of the scale is how many places it may be read or set. Precision is not to be confused with accuracy which is dictated by the the design and the manufacturing process at the time of manufacture. The result taken from an old slide rule may be precise but not accurate. See Accuracy (of a slide rule).

Precision Scale (Company) - Company based in Phoenix, Arizona, formed by Art Eckel in 1948 after leaving Pickett & Eckel , which he co-founded with Ross Pickett in 1943. The all-metal slide rule designs, slightly different than the later Picket models, were aimed at meeting U.S. Government markets. A model 1751 Log Log 10 Hyperbolic was produced as well as an ariel model FAA-164M for Astrodyne (MFR26425) which was also marked US Air Force A-1 Aerial Photo Slide Rule (LM-221A).

Primary Divisions - Those graduations or tick marks on a scale that signify the most significant digit of a number. The Primary divisions are generally the only marks labeled with the numeric value, Integer or Prime Numbers. See Secondary Divisions , Tertiary Divisions and Sub-divisions.

Primary Scales - These are the two scales, usually marked C and D , which take on the initial value of the first known variable X in an equation. All other scales are a mathematical manipulations of the primary scales.

Prime Numbers (slide rule) - The numeric labels, typically, integers, written on the scale of a slide rule corresponding to the major divisions of the scale. The sub-divisions are not normally labeled and must be interpolated by their associating between the prime numbers.

Prime Number (mathematic) - A positive number that can only be divisible or has no factor but itself or 1. Examples: 1,2,3,5,7,11,13,17, 19,23,... etc.

Prince, John Luther - (1941-2005) Professor at University of Arizona, Tucson, AR, man of faith and an avid collector of slide rules. Memorial.

Product - The result or answer from multiplying two terms known as the multiplier and the multiplicand.

Product -1 or Prod -1 - Found on slide rules, c1905-1940 on the right of the lower stator, added as reminders or aids to the operator to keep track of the decimal place. At the left side of the lower stator "Quotient +1 or Quot +1" is found. In the case of multiplication, one determined the number of decimal places in the product by adding the number of decimal places in the two individual factors and subtracting 1 whenever the result was read to the right of the first factor, i.e. the factor on the lower scale. If the product was read to the left of the first factor, then the sum of the decimal places was used unchanged.

Projection slide Rule - An instructional aid that displays the scales of a transparent stock and slide slide rule. Pickett Pr-12 and Post 1447DP are examples of types that use an overhead projector. One attempt was a dedicated projector made by the Italian company Filotecnica Salmoiraghi around 1951, but only 5 were produced.

Proof Rule - Also called the Comparative Rule, used to determine the amount of water needed to reduce the alcoholic content of wine and spirits. One of the earliest uses of a slide rule. One manufacturer was Dring & Frage.

Proportion (Calculating) - In proportion calculations, bring the first term to the slide to the second on the rule and move the cursor to the third on the slide, reading the fourth term on the rule.

Proportional Slide Rule - A proportional slide rule, such as the Pickett 106C, is used in the reproduction industry, where the size of an image is increased or decreased, to maintain the aspect ratio of the original size. Calculations may be performed selecting a percentage or by selecting a change in length of one size of the original to the desired length. The length of the other side will be determined once the percentage is found.

Ps or P - √(1-(0.1x)², Cosine of sin-1D

PS Hairline - Found on some European multi-lined cursors as a conversion factor. PS is the German notation for Pferde-Stärke, translated as horsepower (HP), and is used with the kW hairline in conjunction with the C or D scale to convert kilowatts to British (Metric) horsepower (and BHP to KW). 1 PS - .736 kW. The United States and France use 1 HP = 746 Watts. Put the PS at the right index of C and read the value under KW to see which conversion factor is being used.

Ps scale - √(1-s²), Vector analysis scale (Thornton, etc).

Psychrometric Slide Rule - (also psychrometry) Used in the field of engineering concerned with the determination of physical and thermodynamic properties of gas-vapor mixtures. Typical scales are wet bulb and dry bulf temperatures and relative humidity.

Pt scale - √(x²-1), Tangent of cos-1(1/D).

Pt scale - √(1+t²), Vector analysis scale (Thornton, etc).

Purdue Engineer's Yell - This cheer from the 1960's was contributed by Bruce Chelf, Purdue Alumnus...

e to the x, dy, dx
e to the x, dx
cosine secant tangent sine
three point one four one five nine
square root, cube root, Btu
slipstick, slide rule, Yay Purdue

The ISRM curator subsitutes CSU

PVC - A plastic used in the manufacture of post-war slide rules and currently being used by UTO. PVC, or polyvinyl chloride, is chemically known as (C2H3Cl). Manufacturers gave their own names to special blends of PVC, like Aristopal, Astralon, Anagit and others.

Pyralin - The trade name that Dietzgen used to call the celluloid lamination on their early slide rules.



Q or δ or ρ"- Gauge Mark, generally on the C scale denoting seconds in a radian in the French decimal system 636620 = (200 x 100 x 100)/π. Sometimes described as graduated in the French decimal system.

Q or D scale - Quality factor of capacitance or inductive circuits (capacitance will normally have some resistive factor). A coil always has some losses so Q will always equal something less than infinity [Pickett N16-ES Electronic slide rule].

Q' or δ' (delta') - Gauge Mark, generally on the C scale denoting minutes in a radian 3437.74 = (180 x 60)/π

Q'' or δ" (delta") - Gauge Mark, generally on the C scale denoting seconds in a radian 206265 = (180 x 60 x 60)/π

Q scale - Cosines of angles on Θ or RΘ when left index is under Θ or RΘ, numbered 1 to 10. Also for solving right triangles and Z = R + JX when used with P (Hemmi/Post).

Q' scale - Extension of Q scale, numbered 10 to 14.13

Q1, Q2 scales - Equivalent to a 20 inch scale.

Quotient - The result or answer from dividing one term called the divisor into a second term called the dividend.

Quotient +1 or Quot +1 - Found on slide rules, c1905-1940 on the left of the lower stator, added as reminders or aids to the operator to keep track of the decimal place. At the right side of the lower stator "Product -1 or Prod -1" is found. In the case of multiplication, one determined the number of decimal places in the product by adding the number of decimal places in the two individual factors and subtracting 1 whenever the result was read to the right of the first factor, i.e. the factor on the lower scale. If the product was read to the left of the first factor, then the sum of the decimal places was used unchanged.



R - Gauge mark on early electrical slide rules denoting the resistance of copper conductors at R² = 30.6 This point, along with W, were used regularly by electrical specialists.

R gauge mark - 180/pi, degrees to radians conversion, Value: 5.730*10

R-line - A gauge mark located between 5.7 and 5.75 on the C and D scales of some Chinese Flying Fish slide rules, representing the degrees in a Radian or 52.2958°. It is used to convert radians into degrees using multiplication or converting degrees into radians using division.

R scale - The reciprocal scale is an inverted double logarithmic scale having the same length as the A and B scales, and can be found on early Mannheim slide rules, like the Dietzgen Phillips 1740. Later designs called this scale BI.

RΘ scale - Angle in radians. Numbered 0 to 1.5+ radians.

R1 scale - The square root of D. The R1 scale is the first  half of a D scale doubled in size and the R2 scale is the second half. This allows  greater precession. R1=W1' = W

R2 scale - The square root of D. The R2 scale is the second half of a D scale doubled in size. R2 = W2' = W2.

R% scale - On a commerce or financial slide rule denoting percent markup. The CI scale is also used for this purpose.

Radiac - A type of circular slide rule used during the cold war to determine radiation exposure after a nuclear explosion (do you really want to know at that point?).

Radian - Angular measurement, there are Radians in a circle, or 1 radian = 57.3°

Rafter Framer Slide Rule - See Easterly Rafter Calculator.

Räknelinjal or räknesticka - Swedish translation and usage for slide rule.

Ready Reckoner - The predecessor of the modern slide chart. The term "Ready Reckoner" was probably first coined by an Englishman: Daniel Fenning (1714/15-1767). Fenning was a schoolteacher well-known for his spelling and language aids. He was also a prolific author of textbooks. In 1757 he published: "The Ready Reckoner, or Trader’s Most Useful Assistant". Unlike most calculating aids, Ready Reckoners do not rely on logarithms and are exclusively a printed aid. According to the Oxford Compact English Dictionary a Ready Reckoner is: a book, table, etc. listing standard numerical calculations or other kinds of information. Read David Rance's (NL) paper Reckon on it (2,92Mb Pdf).

Re-branded - The process of adding a distributor's name to a slide rule that was manufactured by another company or OEM (Original Equipment Manufacturer). Many Japanese and German slide rules were re-branded for U.S. companies like Frederick Post, Lafayette, Dietzgen, and many others. There are virtually no other countries that re-branded U.S. slide rules with their foreign counter-parts.

Rechenstab - A German translation of "Slide Rule"

Rechenscheibe - A German translation of a "Circular Slide Rule", as opposed to Rechenschieber, a straight one.

Rechenschieber - A German translation of a straight "Slide Rule", translates as "calculation slider".

Rechenschieber-Sammler (RST) - Translated in English: Slide Rule Collecting Tank. A major German collector group that started in 2001, with membership alliances to the UKSRC, Kring and Oughtred Society. Publishes its newsletter RS-Brief twice a year. The RST web site is in German.

Reciprocal - The reciprocal of a number is found by dividing 1 by that number, as in 1/x. The reciprocal is easily found on slide rules with inverted scales like CI, CIF, BI, DI, etc. CI gives the reciprocal of the number located on C when the indices of the scales are lined up. These scale are generally inked in red to denote that the scale increases in magnitude from right to left.

Red scales - Scales inked in the color red are inverted or reciprocal scales, like CI, BI, DI, etc., but also include The negative log scales like LL00, LL01, LL02, LL03, and complimentary trig scales like COS, SEC T, etc. Generally, a red numbers and graduations indicates that the scale increases numerically from right to left. This manufacturing practice was introduced for quality slide rules in the early 1900's and increases the cost of production with the additional inking pass and masking required. Pickett added a directional symbol "<" to each primary number to remind the user which way to read the scale, whilst K&E and others leaned the numbers in the direction of increasing magnitude.

Redi-Rule - A Dietzgen trademark name for pocket slide rules.

Reed, Joseph Griffith - (1897-1969) A Northbridge, Australia Radio engineer that designed System REED, a set of electro scales used by the Service Slide Rule Company in Sydney, Australia, and wrote the instructions for 'The Reed' electronic engineer's slide rule. Employment was as a Trainee engineer, P.M.G.'s Department, 1913-21; engineer, Coastal Radio Service, 1921-22. Radio operator R.A.N. 1914-19. Engineer, A.W.A. Ltd. (Amalgamated Wireless Australasia), 1922-50. Radio engineer, Overseas Telecommunications Commission, 1950-62. By the 1950's Reed had been granted nine work-related patents for his pioneering radio work. One patent, 116600: "Improvements in radio telegraph transmitters", was incorporated in the high-power equipment used by the U.S. Signal service during World War II and later by the New Zealand Post and Telegraph Department. Portrait

Regla de Cálculo - Spanish translation of "Slide Rule".

Regle A Calcul - French translation of "Slide Rule".

Regnestav - Norwegian translation of a "straight slide rule".

Regneskive - Norwegian translation of a "circular slide rule".

Regolo Calcolatore - Italian translation of "Slide Rule'.

Reiss - East German precision instrument company that was located in Bad Liebenwerda, founded originally in 1882 by Robert Reiss as a mail-order house for office and drawing supplies. Later REISS developed into a well- known maker of precision instruments (eg. theodolites, planimeters, drafting machines) and the largest manufacturer in the region. In 1912 their first REISS slide rule came on the market. Models with extended root-scales (STELLFIX) were made in 1920. This gave a 10" slide rule the precision of a 20". After WWII the company became a GDR-run business and exported slide rules to the eastern and western world. REISS was well known for their beautiful light metal slide rules (eg. PROGRESS, Mod.3223). Plastic (DECELITH = ASTRALON) was used later (eg. DUPLEX, Mod.3227 - With 32 scales it was one of the most "loaded" slide rules ever made.)

Relay, Ricoh - Relay slide rules were manufactured in post-war Japan, originally branded NIKKEI, by Nippon (Japan)Slide Rule Company which was founded c1950. The company then became San-Ai Kekki Ltd. exporting slide rules to the USA as Relay Industrial Company. In April of 1963, the San-ai Group joined with Riken Optical Co. which was founded in 1938 as Riken Kankoshi Co., Ltd. manufacturing sensitized paper manufacturer, to become Ricoh Ltd, a Japanese conglomerate of companies, focused on cameras and office automation as well as being the post-war importer of Coca-cola to Japan. In modern times Ricoh has become a major manufacturers of office copiers and printers. Ricoh supplied Ricoh brand slide rules to the United States (Ricoh Industries, USA) and to European (Ricoh Europe SA in Switzerland) markets and re-branded slide rules to other companies such as: Alvin, Charvoz-Roos, Compass, Dietzgen, Eagle, Engineers, Jason, Lafayette, Lietz, Tobe, Lutz, Fuji, Micronta, Omega, Paleo, Pickett (the B1 only), Relay, Ricoh, Sans & Streiffe, SIC (Scientific Instruments Co), Skyline, SELSI, Staedtler-Mars, J.C.Penny, and Wallace & Wallace. Their quality rivals competitor Hemmi.

Rho or ρ - Small Greek letter ρ or Large Greek letter Ρ.

Richardson, George W. George Washington Richardson, a consulting engineer of Chicago, Illinois, was an ex-Chief Electrician for the U.S. Navy, and designed sheet metal slide rules. His first design, called "The Direct Reading Slide Rule" had a unique calculating system involving holes in the thin stock that matched letters on the slide to speed up common calculations and to perform conversions. Patents issued from 1911 to 1918 were 982,876; 1,021,484 and 1,260,454. Geo. Richardson's created many specialized variations, some for the military, and there is evidence that he consulted for other manufacturers. He co-authored the book The Slide Rule Simplified along with J.J. Clark, which uses his "Pantocrat" slide rule for its examples and is partly a catalog for Richardson Rule Works. The International Correspondence Schools (I.C.S.) in Scranton, PA issue his slide rule as part of the curriculum. George was married to Clara A. Richardson. Retired prior to 1920 after selling Richardson Rule Works to Claire Gilson, founder of Gilson Slide Rule Company.

Richardson Rule Works - An American manufacturer of sheet metal slide rules located in Chicago, Illinois. First known address was: 4212 24th Place, Chicago, then later Machinery Hall, Washington Blvd. and Clinton ST., Chicago. It was founded by George W. Richardson in 1909 and existed until about 1940. "The Direct Reading Slide Rule" had a unique calculating system involving holes in the stock that matched letters on the slide to speed up common calculations and to perform conversions. Geo. Richardson's first design started with aluminum then transitioned to stainless steel. In tha back of the book "The Slide Rule Simplified", Geo. Richardson writes that they make celluloid-on-metal (black on white background) protractors, draftsman scales, transparent triangles and will "manufacture anything requiring Accurate Engine Dividing, Circular or Lineal, Standard or Logarithmic graduations". Richardson used a "Be Wise" owl logo on the back of the manuals that also was used on Gilson metal circular slide rule manuals, so there may be a close business connection. Richardson supplied slide rules to Post in 1921 (pre Hemmi years) for their catalog models 1437, 1437-A,B,C. 1910 Popular Mechanics advertisement

Riehle, Frank - Founded IWA in 1926, in Denkendorf, Germany.

Rietz, System Rietz - An arrangement of scales found on some German made slide rules, defined by Max Rietz. Beside the main scales (C,D) there is a two-cycle (square) scale (A,B), a reciprocal value scale (CI), Logarithmic scale (L) and scales for trigonometric functions (T,S) on the front or on back of the slide. Scales: L, K, A, [ B, CI, C ] D, S, T.

Rietz, Max - (1872-1956) German designer of the System Rietz layout of scales which was patented (DRGM 181110) in 1902.

Roberston, John - (1712-1776) a mathematics teacher at the Royal Academy, Portsmouth. In 1778, John Robertson designed a slide rule utilizing a cursor, or sliding indicator, for use with additional of C and D scales for multiplication.

Roget, Peter Mark - (1779-1869) an English physician and the author of Roget's Thesaurus, invents a log log scale, which he uses to calculate roots and powers to any number or fraction thereof. It is regarded at the time as a mathematical curiosity. Fifty years later, advances in electrical engineering, thermodynamics, dynamics and statics, and industrial chemistry make these scales so necessary they are rediscovered. More Peter Roget Biography (wickipedia).

Roos Company - The Roos Company of 280 Madison Ave., New York, founded by Abel Gottheimer and Ethel R. Gottheimer, partnered with Andre and Angele Charvoz, circa 1941, was a U.S. manufacturer of painted wood and laminated wood slide rules, presumably to fill the void caused by import restrictions during WWII. Frederick Post, Dietzgen and other slide rule manufacturers depending on imports, replaced their Hemmi and Nestler slide rules with Roos slide rules during this time. A reasonable assumption was that Gottheimer manufactured the slide rules and Charvoz handled marketing, as by 1945, The Roos Company was distributing "Charvos" [sic] drawing instruments manufactured by Andre Charvoz, under Charvoz, Inc. Roos products included scales, slide rules, drawing pencils, triangles, protractors and parallel rules. (Roos Company trade literature). After the war, the partnership was dissolved on June 14, 1946 and became Charvoz-Roos Corporation, still located at 280 Madison Avenue. It is possible that plastic parts of Roos and Charvoz-Roos slide rules were made and supplied by the U.S. Company Acu-Rule as many parts are identical with other brands of the time. Early slide rules were identical to Post 1442, 1447-D, 1452-D, 1462 and Henschel 2020.

Rosewood - Rosewood was used by British (English made) slide rule manufacturers, Unique and Thornton for their earlier stocks. Honduras Rosewood is found in Belize, between the Sarstoon and Monkey Rivers and Brazilian Rosewood is found in the Eastern forests of Bahia to Espirito Santo and Rio de Janeiro. Description: Heartwood is shades of reddish to purple-brown with alternating dark markings. Sapwood is yellow. Straight to slightly wavy grain. Medium to fine texture. Low lustre. Honduras is tougher than Brazilian, but not used when strength is important. Heaviness prevents bendability. Blunting effect on cutting edges is moderate. Turnery usage is excellent. Necessary to pre-bore nails. Gluing may difficult due to oil in wood, and does not provide a naturally high finish.

Rotarule (Dempster) - The Dempster Rotarule was an elaborate form of circular slide rule designed by Jack R. Dempster and manufactured out of his home in Berkeley, California from about 1928 through 1948. Two models were produced starting with the model A and finishing with the model AA and 2500 of these were sold. The slide rule was made from a light synthetic material and answers are obtained by the use of revolving discs and a single indicator. It has several spiral scales which permit greater precision. A Dietzgen catalog has the Rotarule as model 1798 and describes it thusly: "A 5 inch diameter rule fitting the coat pocket, provided with 13-inch scales for rapid work and 50 inch scales fro extremely accurate multiplication and division. The 50 inch-inch length obtained by coiling the scales 4 times around the dial in spiral form, permits readings to 4 figures even at the upper end of the scale. 5 figures may be read at the lower end by close interpolation. Front Scales: Cubes, Squares, Numbers, Reciprocals, Folded Scale, 17 inch trigonometric scale (all 6 functions) and Stadia scale. Back scales: A pair of spiral scales of 4 coils each, Log Log scale of 4 coils, Common Logarithms, scale for finding √(x²+y²) in one setting.

Rotorule (Boykin) - A sophisticated circular slide rule, designed and manufacturered by Bernard C. Boykin in Ruxton, Maryland from 1957 through the 1970's. Only 200 units were sold, making this very rare. It is similar to the earlier Dempster Rotarule (note slight spelling difference, Rota vs Roto), which was produced up to 1948, but with less scales and a modified scale arrangement.

Routledge, Joshua - (1775-1829) England. Invented the Routledge two-foot, folding Engineers Slide Rule, made of boxwood, in 1809.

Roylance Electrical Rule - The Roylance K&E N4133 is a special Polyphase type rule designed by K&E that makes it possible to solve many electrical problems directly by the use of special scales and gauge marks. It has extra hairlines on the indicator to calculate circular areas directly.

RST - See Rechenschieber-Sammler (RS-Brief) English: Slide Rule Collecting Tank. A German collector group.

Rubber Slide Rule - Term used by engineers to force "the numbers" to fit, when management needs to justify a project.

Runner - Another name for the sliding cursor or indicator, used by K&E and others. See Cursor

Russian (Soviet) Calculators - The first mechanical device used in Russia for computational purposes was the Russian abacus called Schoty. This device became "the national calculator" and was used in cashier's offices down to the middle of the 90's. It is interesting to note that the textbook "Trade calculations" published in 1986 devotes a whole chapter to methods of calculation by using abacuses. Simultaneously with the abacuses, still during the pre-revolutionary years (1917), the logarithmic (slide) rules were used in scientific circles, practically without change, since the 17th century. They were in service "serve smb. faithfully" up to the appearance of electronic calculators. In an effort to automate the processing of calculations, the mankind begins to invent mechanical calculating devices. It is known that the Russian mathematician Chebyshev designed a calculator at the end of the XIX century, unfortunately the drawings were lost. Contributed by Sergei Frolov.



S or s hairline - Found on some European multi-lined cursors. Used in conjunction with the D hairline (may be located at the center hairline) to determine the area of a circle. Placing the D (or d) hairline over the diameter value on the C or D scale, the area of the circle is found under the S (or center) hairline on the A or B scale. Example: Position the D hairline over 4 on the D scale, read 12.6 on the A scale under the center or S hairline.

S-line - A gauge mark on Chinese Shanghai Flying Fish slide rules for finding the area of a circle (A=d²π/4) when its diameter is known. Same as π/4 on many others. The S-line is engraved on the A and B scales between the numbers 78 and 79, equal to π/4 = .786. Using the hairline, set the right index of the C scale on the S-line and for any diameter on the C scale, the Area may be found above on the A scale.

S scale - sin-1x, D is the sin of the angle S. If S is on the slide then the ends must be lined up. Read the angle of the sine or cosine on the S scale (keeping in mind that angles for cosines increase to the left) and read the result from the D scale.

S1 scale - sin-1x, for sines of angles 5°45' to 90°

S2 scale - sin-1x, for sines of angles 35' to 5°45'

S or ρ' - Gauge mark same as  Q" or δ",  denoting seconds in a radian 206265 = (180 x 60 x 60)/π

Safety Factor - See Factor of Safety.

Sama & Etani, Inc - Sama & Etani Inc out of Groton, Massachusetts was founded by Dominick Sama and Kenji Etani who designed and distributed custom data chart incorporating circular slide rules in North America that were manufactured by Concise of Japan. Their most successful designs were like the Data Center with its multiple slide out cards containing the Periodic Table of the Elements and other math related reference tables. Sama and Etani dreamed up the idea of the data chart rules, and metric factors designs as part of their business school thesis, speculating they might be able to sell 30,000 pieces. They wound up selling more than a million units, and their logo-marked rules were incredibly popular and widely used in many industries as promotional items.

San-Ai Keiki Co. Ltd. - Previously Nippon Slide Rule Company. Sold slide rules under the Relay brand, until merging with Ricoh Ltd. Relay/Ricoh was a close second to Hemmi in producing high-qualilty bamboo slide rules. Some of their high-end rules, both duplex and simplex can be found to rival Hemmi in workmanship, but sales of the company were so far behind Hemmi that good specimens of Ricoh rules, particularly their high-end slide rules, are quite rare. ref: William Lise.

Sans and Streiffe - An American optical equipment supplier, located in Brookfield Illinois. A re-seller of Japanese optical equipment like binoculars and microscopes as well as slide rules made by Relay/Ricoh. the 311's and 312's are re-numbered Relay 150 and 151's. Known date codes range from 1959 through 1971.

sc scale - sin.cos, Sine x cos, used in tachometric (stadia) calculations.

Scabbard - The protective sleeve or case used to store individual slide rules. Some leather variations for the United States market had belt loops reminiscant of holsters. Leather sleeves were necessary to sell complex slide rules into the U.S. by German and Japanese importers.

Scale - The logarithmic interpretation of numbers engraved in various formats onto a slide rule to enable different calculations to be performed. (Peter M. Hopp)

Schoty (Russian Abacus) - (pronounced SHAW-tee). It was invented in the 17th century and is still in use today. The abacus is operated by sliding the beads right-to-left. The Schoty does not have the central bar. The unit beads are colored light and the '5' the middle are dark. The design of the schoty is based on a pair of human hands. If you hold out both hands in front of you, palms facing out, you will see that your 2 thumbs are beside each other and 2 sets of 4 fingers spread out from there. Similarily, on the schoty, each row has 2 sets of 4 beads of the same colour on the outside, representing the 2 sets of 4 fingers and the 2 innermost beads of the same colour representing the 2 thumbs. The "home" position for the beads is on the right hand side. The bottom-most row represents 1s, the next row up represents 10s, then 100s, and so on. So, counting is similar to counting on one's fingers, the beads move from right to left: 1 to 10, and then carrying upwards to the next row. The Schoty abacus frame is generally wooden, early models made of oak and later models made of birch, with wooden beads on curved steel rods. The rods are intentionally bent in the shape of a slight arc so that when the beads are moved from side to side, gravity will keep them in place.

Schuitema, Ir. IJzebrand - (1929-2013 ) A prominate Dutch slide rule collector and author of several technical and historical publications about slide rules and history, the most known is Calculating on Slide Rule and Disc September 2000 and May 2003, Astragal Press, coauthored with Herman van Herwijnen. Graduated as a Civil Engineer from the Technical University Delft, South Holland, the Netherlands. Retired in 1986 from a career in civile engineering, management and university lecturer. Member of the Dutch Circle of Slide Rule Collectors and one of the world's foremost authorities on the subject of slide rules.

Schwartzer, A.R.(Dick) - (3-5-1933 to 3-11-2005) Professional Electrical Engineer. Retired from the Salt River project in Arizona in 1991. Founder of the Slide Rule Emporium in Scottsdale, AZ, and collector of scientific instruments, he had the foresight to recover all of Pickett's slide rule inventory out of Mexico, before they were to be scrapped for the aluminum, when the calculator created the demise of the slide rule industry. In the last years, even though wheel chair bound and on oxygen, Dick faithfully maintained sales of NOS Picketts out of his home until his death.

Scientific Instruments Co. (SIC) - A Berkeley, California Slide Rule company founded by Fred Ellis, that was in business from about c1950 to c1970, that sold S.I.C. and SINCO branded linear slide rules from Relay/Ricoh (San-Ai Keiko, Ltd) and circular slide rules from Concise as well as manufacturing their own brand called Roto Rule. SIC had custom models which added cursor scale labels on the lens, a handy, yet costly, technique which was never duplicated on other brands or by other manufacturers. They are credited by some collectors and historians to have made the Pickett line of metal circular slide rules, others say that Concise was the possible manufacturer.

Scientific Notation - In scientific notation every number is expressed as a a number between 1 and 10 followed by 10 raised to a power. With a slide rule, only the first two or three significant digits of a number, expressed in scientific notation, are calculated and the operator must keep tracks of the number of decimals places. Modern students with calculators have lost the 'feel' of a result, whether the answer makes sense, or not (in Mike Konshak's opinion).

Schooley Engineering Company - Out of Terril, Iowa. Advertised in Popular Mechanics Magazine in March 1936 for a "Slide Rule with Instructions" for a price of $1.00. Most likely it would have been a rebranded slide rule, but it is unknown at this point who the manufacturer was.

Sd scale - α/sinα, Sine differential scale, for sine range 0° to 90°. (PIC/Thornton)

Sears & Roebuck Company - American catalogue company that sold slide rules that were manufactured by Relay/Ricoh (Japan) and were re-branded with the proprietary Tower brand.

Secondary Divisions - Those graduations or tick marks on a scale that signify the second significant digit of a number. Secondary divisions are only labeled with the numeric value on when space allows. See Primary Divisions , Tertiary Divisions and Sub-divisions .

Sector, The - The sector was invented by Thomas Hood in 1597, and independently by Galileo in 1606, and used for the solution of specific problems. Also in 1606, it was proposed by Edmund Gunter as a general calculational tool. An early fore runner of the slide rule which solved multiplication and division problems by proportionality of angled lines and works on the principle of similar triangles. The instrument consisted of two equal rulers movable about the center of a joint. A pair of dividers is necessary to read the relationships on all sectors. Sectors were made with a variety of scales for use in calculation by navigators, surveyors, gunners, and draughtsmen. At first sight they look like a jointed rule usually made of ivory, brass, wood, or sometimes silver.

Seehase, Dr. Ing Hans - German Engineer. Invented a inexpensive generic slide rule design made of cardboard/celluloid, similar to slide charts, which was suited for making promotional rules that were branded with Germany, US and UK firms (known examples). The patent application was made in Germany on 28 March 1939 in the name of Dr Ing. Hans Seehase; the patent number DE727007 was granted on 8 March 1940 and published in 4 September 1944. Given what was happening in Germany at that time it is interesting that the process of publishing the patent still continued. (Note: Antwerp was freed by a British tank division on the day the patent was published. per Rod Lovette) Dr Seehase had another patent for slide rules granted in 1956. In 1937 proposed and designed a human powered plane similar to the modern Gossamer Condor, which was built 40 years later.

Sella, Quintino - (1827-1884)- The logarithmic slide rule was first introduced in Italy in 1850 by Quintino Sella , a Minister, a mountain climber and an engineer from Biella. His Theory and Practice of slide rules was first edited in 1859 by ed. Stamperia Reale, Turin.

Selsi Company, Inc. - A current US importer, founded 1854. Imported optics such as binoculars and telescopes as well as watches and clocks. In 1929, the business was incorporated and became known as Selsi Company, Inc. The name was derived from combining the founding partners' initials with two vowels. Selsi had been one of Sussfeld, Lorsch and Schimmel's trade names, and had been used on its products for many years. Re-branded and sold Relay Slide Rules under the Selsi name, c1959.

Service Slide Rule Company - Sydney, Australia. Made two slide rules similar in construction to Unique in England. Their Electro model and System REED, the later using scales designed by Joseph Reed, a radio engineer. The company appeared in the Sydney telephone books from 1954 through to 1987. In 1976 the entry was: Service Rule Co. (Stan Bernacki) 45 Stanley St, Peakhurst, a suburb of Sydney. In 1987 it had moved to 58 Barry Avenue, Mortdale, another suburb of Sydney. Stan Bernacki is assume to have been the owner.

Set, Setting - To set a slide rule means to place a given number on one scale over a another given number on another scale. To position the hairline over a given number on a given scale.

Sh scale - This is for the sinh (hyperbolic) function. Sinh is directly read from the D scales for angles in radians.

Sh1 or Sinh1 scale - sinh-1x, Θ(0.1 to 0.9). Read Θ on Sh1 and value of SINH Θ (0.1 to 0.9) on D. Found on vector slide rules like the 1933 K&E 4093-3 Log Log Vector Duplex.

Sh2 or Sinh2 scale - sinh-1x, Θ(0.9 to 3). Read Θ on Sh2 and value of SINH Θ (1 to 10) on D. Found on vector slide rules like the 1933 K&E 4093-3 Log Log Vector Duplex.

Shanghai Ding Feng - A Chinese factory and brand of slide rules that were manufactured in Shanghia, China. Shanghai Ding Feng which was a joint private-state owned factory which later changed its name to Flying Fish Slide Rule Factory.

sh.d scale - Reference to the old British pre-decimal coin system. sh being 'shillings' and d being 'pence'. There used to be 20 shillings to a pound (£), therefore the the scale reads 0 to 20, and 12 pence to a shilling. These designations, along with the £ symbol were quite common on European business rules, often in combination with percent, interest or compound interest scales. Because it was not a decimal system, calculations involving parts of a monetary Pound had to be converted to a decimal of a Pound before they could be calculated on a slide rule. Hence the conversions on the log 10 scale. See British pound (£) scale

Sheahan, N. Thomas - Designed the Ground Water Hydrology Computer in 1967 while working as a Research Geologist for Layne Associates, Research Division, Memphis, TN. Tom Sheahan retired as a Senior Consultant Hydrogeologist from AMEC Geomatrix, Murrieta, CA, in 2008.

Short Base Triangulation Slide Rule - A slide rule used by the military to determine range, elevation and azimuth to a target. The scales are marked in yards-Meters-Mils. See Mil-Radian. K&E produced one in 1947 and an earlier 1917 example was made by Geo. Richardson Co. For J.H Weil & Co.

SKALA - A brand of slide rules made in Poland.

SI (International System of Units) - SI is a modernized version of the metric system established by international agreement. SI provides a logical and interconnected framework for all measurements in science, industry, and commerce. The metric system is much simpler to use than the existing English system since all its units of measurement are divisible by 10. The SI system is founded on seven base units for seven base quantities assumed to be mutually independent, as given in length=meter[m], mass=kilogram[kg], time=second[s], electric current=ampere[A], temperature=kelvin[K], amount of substance=mole[mol] and luminous intensity=candela[cd]. Other derived units with special names are the liter, radian, hertz, hectare, newton, pascal, coulomb, volt, farad, ohm, watt, seimens, weber, tesla, henry, degree celsius, lumen, lux, becquerel, gray, sievert and katal. In SI, most quantities can be expressed in multiple or fractional terms according to the order of magnitude, using the base10 numbering system. For example, attaching the prefix "kilo-" to a unit increases the size of the unit by three orders of magnitude, or one thousand (103). Attaching the prefix "micro-" to a unit decreases the size of the unit by six orders of magnitude, the equivalent of multiplying it by one millionth (10-6). See Metrification.

SI1 scale - Two adjacent scales with a range of COS 5.74°-0.575° and SIN 84.28°-89.425°. Found on the slide of the 1933 K&E 4093-3 Log Log Vector, which introduced decimal trig scales. Used in conjunction with their SI2 and TI scales. Both SI1 and SI2 scales doubles the resolution of the standard S scale of 5.72°-90° located on the stock with a T scale 5.72°-45°

SI2 scale - Two adjacent scales with a range of COS 90°-5.74°) and SIN 455.72°-84.28°, Found on the slide of the 1933 K&E 4093-3 Log Log Vector, which introduced decimal trig scales. Used in conjunction with their SI1 and TI scales.

Both SI1 and SI2 scales doubles the resolution of the standard S scale of 5.72°-90° located on the stock with a T scale 5.72°-45°

S.I.C. - See Scientific Instruments Company.

Simplex - A single sided slide rule, generally a closed body but sometimes referring to an open-body rule with a wrap-around cursor with scales only on one side.

Simplon - Product line name of slide rules made by Dargue Bros. at their Simplon Technical Instrument Works,in Halifax, England. Models included the of the simplex 'Primary' and the 'Bi-lateral' slide rule. These rules are based on a 1934 patent and the Bi-lateral has scales on both faces of the plastic covered mahogany stock with a reversible cursor, a predecessor of the duplex style. The stock had two parallel grooves for the runner (cursor).

Sines and Tangents (Calculating) - To find the sine of an angle on a Mannheim closed body slide rule, reverse the slide so that the trigonometric scales are uppermost with the A and D scale and the end divisions are on the slide coincide with the indices on the body. The sine is read off on A over the given angle on S. Read off on D the given angle on T. On more modern duplex slide rules, the S and T scales may be placed on the same surface as the A and D scales or accessible by the doubled sided cursor.

SINCO - An early or alternate logo for S.I.C. or Scientific Instruments Company. See Scientific Instruments Company.

Skid Stick - The title of a slide rule newsletter published by the UK Slide Rule Circle.

Skyline Distributors Inc. - A company based in Denver, Colorado (referring to a 1955 catalog) that sold Surveying Instruments and Supplies including transits, levels, slide rules, tripods, as well as drafting supplies like polar planimeters, proportional dividers, beam compasses, triangles, etc. A branded Skyline Model 151 Technolog was made by Ricoh in Japan and date stamped P.S-4 which was made in 1967.

Sleeve - The protective scabbard or case used to store individual slide rules. Some leather variations for the United States market had belt loops reminiscent of holsters. Leather sleeves were necessary to sell complex slide rules into the U.S. by German and Japanese importers.Most sleeves were made of paper board, then later injection molded cases, typical of European brands, were supplied with slide rule sets.

Slide - The center portion of a slide rule that extends the length of the Stock or Body. The slide may have scales on both sides.

Sliding Rule - This term, which later became more commonly just "Slide Rule", is credited to Thomas Everard who first used it to describe his excise calculating instruments around 1775.

Slide Rule -The term applies to all instruments designed so as to allow relative motion between the indices and the scales whether they be straight, circular, spiral or cylindrical, and log-log. Once widely used for rapid, approximate scientific and engineering calculations, a slide rule is an analog computer consisting of three interlocking calibrated strips. The central strip can be moved lengthways relative to the other two. A sliding cursor with an alignment line can record an intermediate result on any of the scales.

Slide-rule General - A military leader who takes an intellectual or theoretical approach to war; a military leader who prefers high-tech weaponry and tactics over traditional military doctrines. A phrase coined by US Secretary of State Colin Powell to describe Paul Wolfowitz, the Bush administration's hawkish Deputy Secretary of Defense (1995). Powell actually used the phrase slide-rule prodigy in his book My American Journey (Random House, 1995),

Slide Rule History - Slide rules came into wide use in the 1850s, as engineering became a recognized professional activity. See Engineer. Throughout the 1950s and 1960s the slide rule was the symbol of the engineer's profession in the same way that the stethoscope symbolized the medical profession. Some engineering students and engineers actually carried 5 inch pocket slide rules in their belts (associated with Geek) in addition to using a 10 or 20 inch rule for precision work at home or at the office. All this came to an end in the 1970s, when the advent of miniaturized scientific calculators made slide rules obsolete. See HP35 and Historical Developments in the Evolution of the Slide Rule.

Slide Rule - Psalm/Poem - (circa 1960) Author Unknown, reprinted in FLUE PIPE, October 2003 Newsletter of the American Society of Heating, Refridgeration and Air Conditioning Engineers, Inc., Shreveport, Louisiana Chapter.
There are many like it, but this one is mine
My slide rule is my friend
And I shall learn to love it like a friend.
I will obey my slide rule.
When my stick tells me that 5x5 is 24.8,
Then, by gosh, five times five is twenty-four point eight!
I will learn the anatomy of my slide rule:
Though I die in the struggle, I will use every side,
The black scale and the red, the inverted "C" and the inside out log.
The reversed "A" and the mutilated "D".
I will master them all and they will serve me well, they will.
I will cherish my slipstick and never shall profanity sear
it's long, graceful mahogany limbs.
My slide rule shall be my brother in suffering through
long hours of midnight toil.
We will work together, my slide rule and I.
And on the great day when my slide rule and I have
finished our appointed task
And the problems are done and the answers are right
I will take that darned stick and have one heck of a fire, I will!

Slide Rule - (In) Song - Sam Cooke wrote a slide rule into his lyrics for Don't Know Much about History...
Don't know much about history
Don't know much biology
Don't know much about a science book
Don't know much about the French I took
But I do know that I love you
And I know that if you love me too
What a wonderful world this would be

Don't know much about geography
Don't know much trigonometry
Don't know much about algebra
Don't know what a slide rule is for
But I know that one and one is two
And if this one could be with you
What a wonderful world this would be

Now, I don't claim to be an "A" student
But I'm trying to be
For maybe by being an "A" student baby
I can win your love for me

Slide Rule World Records - Attempts to get into the Guiness book of world records by making the longest working (however impractical) slide rule.

  • 20 feet long overall weighing 110 lbs. constructed in 1973-74 by Ralph Nyberg and members of the Mathematics Club of Roanoke-Benson High School, Illinois. Guiness Book of World Records, 1976, Sterling Publishing Co, New York, NY USA.
  • 59 feet 1 1/4 inches in length designed by Ralph J. Snelson and R. Clayton Brough and built by students at Springville Junior High School, Springville, Utah. Guiness Book of World Records, 1978, Sterling Publishing Co, New York, NY USA.
  • 320 feet 11.1 inches in length completed in March, 1979, by students of Alvirne High School, Hudson, New Hampshire. Guiness Book of World Records, 1980, Sterling Publishing Co, New York, NY USA.
  • 323 feet 9.5 inches in length completed on Nov 11, 1979 by Greg Maggs and Robert Kolstad at the University of Illinois College of Law Building in Champaign, Ill. Guiness Book of World Records, 1983, Sterling Publishing Co, New York, NY USA.
  • (currently) The World's Longest Slide Rule, The Texas Magnum, was demonstrated on February 28, 2001 in the Lockeed-Martin Aircraft Assembly Facility at Air Force Plant 4 in Fort Worth, Texas. The Texas Magnum is 350 feet 6.6 inches and holds the world's record for the longest linear slide rule. Co-designers Skip Solberg and Jay Francis. The Texas Magnum was designed as a traditional Mannheim style slide rule. The A, C, D and L scales are included on the slide rule.

Slide Rule & Scale Engineering CO. Inc - A US slide rule manufacturer founded founded by George L. Lockhart in Laporte, Indiana in 1930, and later New Carlisle, Indiana. SR&SE made custom slide wood slide rules, such as the Concrete Quantity Calculator, as well as a standard Mannheim with A-B-C-D-K & L scales. Rules were manufactured using magnolia wood, finished white with an Ethyl-Cellulose base, then printed. A transparent lacquer coating was then applied to protect the printing. In 1945 a facility was built in Mt. Olive, Illinois. On February 14, 1947 the biggest fire in Mt. Olive history destroyed part of the factory. Production resumed in remaining buildings. On April 14, 1950 the company was declared bankrupt. Nicholas Muschong, a Vice president of Acu-rule, filed to do business in Illinois, and may have acquired the assets and copyrights. Similar in design and construction to Lawrence Engineering Services and Festus (Later Acu-Rule) Manufacturing. Other calculator models advertised in a 1940 flyer were Concrete Block and Mortar, Brick and Hollow Tile, Lumber, and Galvanized Sheet Steel Weight.

Slide Rule Tuning Dial (Radio) - This term generally refers to the pre-digital electronic radio industry where the frequency was selected by a horizontal dial scale, as opposed to a circular rotating dial, with division labels indicating the radio frequency (or channel). The hairline was pulled across the dial by a cord wrapped around pulleys and the knob. Most shortwave radios and transmitters with multiple bands used this technique but these tuning indicators offered little more than "hit or miss" tuning accuracy. A 'cat's eye' indicator which helped dial-in the peak signal was required. Major advances in communications receivers during the 1970's including frequency synthesis and digital frequency readout made communications receivers easier to use.

Slipstick - Engineer slang for Slide Rule.

Slipstick, UBC Yearbook - The Slipstick, the engineering yearbook, at the University of British Columbia, is considered one of the oldest, longest lasting traditions of the Engineering Undergraduate Society. They have copies of each Slipstick made throughout the years, starting all the way back to 1949. The last year that a slide rule was pictured on a yearbook cover was 1981, although 1983 showed a logarithmic scale next to each other. By then the current crop of freshman students were asking what 'Slipstick' meant. Photos of all graduating engineering students are printed, as well as pages from events and each Engineering department. Each graduating student is provided one as a part of their grad package, and undergrads can buy them at a reasonably low price by the end of the school year.

Slipstick Libby - A character from Robert A. Heinlein's Methuselah's Children, The scene: It's the early part of the 21st century and a group of refugees have stolen Earth's second interstellar vessel in order to escape from persecution at the hands of the government. The ship is designed to carry a large crew on a lifetime long voyage to a nearby star, but happily one of the refugees is the famous Slip-stick Libby, a natural genius in physics and mathematics. Libby has cobbled together a faster-than-light drive from some spare parts and the ship is now diving into the sun. The reason for this is that the drive needs energy from the sun's gravitational field. Naturally the calculations are delicate, but Libby is a genius with mental arithmetic. The name slipstick refers to Libby's trusty slide rule, which he artfully uses to make the last minute calculations!

Sly-Drooler - A collector of slide rules.

S-M slide rule -  See C.V. Ore.

Smith, W.H. - A British manufacturer of slide rules. The W H Smith rules were based on the Blundel-Harling rules current at the time including 800 series rules, S prefixed rules and the Super Duplex A505. The latter had replaced the similarly designated Academy Duplex A505 rule. There were also two versions of the A506 vector duplex rule and similar changes are found in the special P series rules made for customers such as Paper Facts & Figures and the Met Office.

Snodgrass, BurnsUnique in Brighton (UK) in 1920 which manufactured slide rules until 1975. Burns Snodgrass was also the author of Teach Yourself the Slide Rule.

Soho - The French Soho rule, was the most common slide rule in France until the Mannheim was popularized. Made of boxwood without a cursor, the Lenoir's made them the during the first half of the 19th century. The firm was renamed Gravet-Lenoir (after the Lenoir's death), which then became Tavernier-Gravet (T-G). 30 Rue Babylone is the earliest address for Tavernier-Gravet. Scales: A [ B, B ] D // [ S, T, L ]. Contemporary documentation show that the A/B B scales are the standard ones for normal computations, with the D scale being called the "square root scale". One advantage was that one has the whole S range on one scale. Soho's were still being manufactured in the 20th century, as slide rule collector Ron van Reit has a T-G Soho dated April 1910.

Speed Rule - A slide rule whose selection and placement of scales facilitates speedy and accurate computations. For example, a speed rule might have the C and D scales, or K scale duplicated on both sides of a duplex rule.

Sperry, Elmer Ambrose - (1860-1930) Born in Cortland, NY. Graduated Cornell University 1878 and 1879. Invented the Sperry's Pocket Calculator (c1903) which was marketed by K&E as model 4017. Elmer Sperry was issued US Pat #773,235 on Oct 25, 1904 for this pocket watch slide rule (one of over 400 patents). An entrepreneur, his companies included Sperry Electric Company (1880), Sperry Electric Mining Machine Company (1888), Sperry Electric Railway Company (1884), Chicago Fuse Wire Company (1900), Sperry Gyroscope Company (1910), and the Sperry Corporation. His gyroscopic compasses were used by the U.S. military in both world wars. USS Sperry (AS-12) was named for him. See Wikipedia.

Sperry's Pocket Calculator - Designed by Elmer A. Sperry (c1903) and marketed by Keuffel & Esser as the 2-1/8" diameter model 4017, US Patent #773,235. 1913 K&E catalog description: "Sperry's pocket calculator is a compact reliable instrument which, on account of the length and arrangement of scales gives results that compare favorably with those obtained on a 20" straight slide rule. the instrument has the form of a watch with a glass-covered engraved metal dial on each side. One dial has a three fold scale, while the other has a two-fold scale, a single fold scale and a scale of equal parts. A pointer (hand) coo-operates with watch dial, and there is an index line on each glass cover. the two dials are revolved together by means of the milled thumbnut, and the pointers by means of the smaller knurled knob. There is a small ring on the case for attaching the instrument to watch chains."

Spiral Scales - Found on circular slide rules like the Fuller and Otis-King and on pocket watch slide rules like the Sperry, K&E and Russian KL1 pocket Calculators. The design allows for very long scales and higher resolution than conventional linear slide rules.

Springy-Stocks - Term used to describe closed-body slide rules stocks that are split down the length of the stock and joined together with a thin metal or plastic insert that acts as a tension spring. This technique allows the well to expand and maintain tension on the slide to keep the adjacent scales close together, even if the stocks, typically made of wood, were to swell or shrink. First invented by A.W. Faber in 1907 which used thin spring steel washers as inserts, Faber and D&P (Aristo) also used celluloid sheets imbedded in the floor of the stator. SUN-Hemmi used aluminum sheet to join their slide rules. Adjustment screws were used in some models in place of springs to accomplish the same goal of maintaining the slide alignment.

Sq1 or √scale - Square and square roots, numbered 1 to 3.16.

Sq2 or √ scale - Square and square roots, numbered 3.16 to 10.

Squares and Square Roots - Squares are found by setting the cursor on D and reading the square on A. Square roots are found by setting the cursor on A and reading the root on D.

Snodgrass, Burns - (1886-1954) M.B.E, A.R.C.Sc. Founded The British UNIQUE Slide Rule Company in 1920 . while a mechanical engineering lecturer at Brighton Technical College. Unique specialized in a wide range of wood slide rules with celluloid covered paper scales and were most popular within the United Kingdom, and its colonies. The manufacturing process used fairly basic woodworking tools and printing presses, unlike their high end competitors which had mechanical tooling to make machine divided scales. This made possible relatively inexpensive slide rules that could also be customized to a broad spectrum of industries. The first Log Log slide rules were made around 1928-1929 and sold for 12 Shillings in 1931. Burns made these by himself on a part time basis until 1935, where he added a couple of employes, along with his son. In 1945, the last year of WWII, they sold 100,000 slide rules. In 1951 they became the Unique Slide Rule Company, Limited. Burns Snodgrass was also the author of Teach Yourself the Slide Rule ©1955 which was published in 1955, one year after his death. The book was popular for use in many schools and with other makers, although the graphics referred only to the UNIQUE brand. In 1954, The company was subsequently managed by his son, Donald Clayton Snodgrass.

Snodgrass, Donald Clayton - (1919 - 1993) Son of Burns Snodgrass. He took over management of the UNIQUE Slide Rule Company in 1954, when his father died. After an illness in 1981, Donald retired and his wife, Elain Snodgrass, took over as Managing Director. Various relatives worked in many aspects of the company making this a classic family business, much like all the other silde rule companies. It is estimated that they sold more slide rules in the UK more than any other maker, 2.5 million or more. In spite of their cheapness, older wood versions have survived in large numbers. They invested in all plastic slide rules in the early 1970's but found themselves, like other slide rule makers, obsoleted by the electronic calculator, and stopped production in 1975. They continued manufacturing other mathematical instruments as "Unique Instruments Limited" up until 1993 when Donald Snodgrass died..

SRT, S&T or ST scale - Sin-Radian-Tan x or Sin-Tan x Scale of sines/tangents on the slide. Used to determine sines and tangents of angles between 0.57 and 5.7 degrees. An extension of the S scale, which precedes the S scale values. The sines and tangents are nearly equal so that a single scale can be used for both. The tangents of angles between 84.3° and 89.43° can be read if the complement of the angle (90° - angle) is set on this scale. Read tangents (from 10 to 100) on the CI or DI scale.

ST (or SRT) scale - 180x/π, D radians in degrees. Note: Max Rietz added the ST scale for small angles, and the inverted CI scale in 1925 to the arrangements he first described in 1902, which included the A, B, C, D, K and trig scales S and T. This scale arrangement became known as "System Rietz".

Stadia - A special type of surveying rule (ex: K&E 4100) for surveyors to use in the field with scales for both horizontal and vertical distances. Also called a Tachymeter Slide Rule. It is based on two equations:
   Horizontal distance = rod reading x (cos2α)
   Vertical distance = rod reading x (sin 2α)/2

Staedtler, Staedtler-Mars - American drafting supply company and re-seller of slide rules, made by Nestler (Germany), Relay/Ricoh and Fuji (Japan).

Standard Length Slide Rule - See 10 Inch Slide Rule.

Stanley, William Ford Robinson - (1829-1909) Holborn, London. Founded W.F. Stanley and Company, manufacturers of mathematical, drafting and scientific instruments in 1854. It became a limited liability company in 1900. In 1861, Stanley invented a prize-winning straight-line dividing machine that was used to make accurate scales for slide rules and other mathematical instruments. Among the slide rules manufactured were the Cooper 100 Inch Slide Rule (1923) and the Fuller spiral slide rule.

Stator - Another name for the non-moving stock or body of the slide rule. See Body.

Sterling Plastics - An American company, owned by George and Mary Staab of Mountainside N.J. that entered the slide rule business after buying the the Acu-Rule Mfg, Mt. Olive, Illinois on June 25, 1968. In 1969 the operation was moved to Sheffield St., Mountainside N.J. 07092. Sterling was purchased by Borden Chemical Company around 1970 and the Sterling Acu-Math brand was being sold as late as 1972.

Stifel, Michael - (1487-1567 Jena) An Augustine monk who first developed the idea of logarithims. Stifel was, next to being a cleric, an inspired mathematician. Originally a Roman Catholic, in around 1521 he aligned his thinking with the doctrine of Martin Luther, with whom he had a close personal contact. In 1524 Luther arranged for him to be nominated as court chaplain to Count Albrecht von Mansfeld in Wittenberg. For the first few years he battled with the conflict between Roman Catholicism and Reformation. In 1535 it was Luther again who nominated him in for a post in Holzdorf. There he had the best and most fruitful twelve years of his scientific life and devoted all his energy and attention to mathematics. It was during these years, in 1543, that he published his Arithmetica integra. It was intended as a text book for students, but it turned out far too difficult. In this book he dealt with many subjects. He introduced the notion "exponent", designed the symbols "+" and "-" for addition and subtraction; the fraction line; the "=" symbol for "is equal to" and calculating with negative numbers. The most significant for us are the two lines of numbers positioned above each other. One was an arithmetical series and the other a geometrical series. The upper row were indexes to the power of 2. While the lower row depicted the values of these powers. This was an important contribution to the underlying idea of the logarithmic calculating system.
-3 -2 -1 0 1 2 3 4 5 6
1/8 1/4 1/2 1 2 4 8 16 32 64
(ref:IJzebrand Schuitema, The Slide Rule Technical Cultural Heritage, 2001)

Stock - Another name for the non-moving stator or body of the slide rule. See Body.

Straps - The brace or bridge that holds the two pieces of the stock of an open framed slide rule in parallel.

Studio - A model of an Aristo slide rule intended for students.

Sub-Divisions - the smaller spaces, tick marks or graduations on a scale between the major or prime numeric values, also called Primary Divisions. Generally the longer the scale the more sub-divisions between the numbers. After the Primary divisions are the Secondary divisions, then the Tertiary divisions. The sub-divisions of the 5 inch rule range from 50 to 10 between the prime numbers (those numbers actually written on the scales). The 8 inch rule is divided twice as close as the 5 inch rule having subdivisions ranging from 100 down to 20 between the prime numbers. The 10 inch rule, considered standard, is sub-divided the same as the 8 inch. The 20 inch rule is sub-divided more closely than the 8 and 10 inch rules, having sub-divisions ranging from 200 down to 50 between the numbers.

Sun - Hemmi's trade name for their own slide rules. See Hemmi.

Surveyors Duplex Rule - This special rule (ex: K&E 4102) reduces complicated spherical-trigonometric calculations of astronomical data, essential to surveying, to mere mechanical operations.

System Rietz - Slide rule scale arrangement: See RIETZ.



T scale (double) - Tan-Cot x, Tangent scale, gives tangent of angle Θ (degrees) or RΘ (Radians), numbered 5.73° to 84.28°. The "double scale" arrangement has the angle set above the line if it is between 5.7 and 45 degrees, and below the line if it is between 45 and 84.3 degrees. Tangents are then read on the C or D scale, and cotangents read on the CI scale. Note that the CI scale is often NOT present in a way that permits this setting on one side.

T scale (single) - Tan-Cot x, Tangent scale, gives tangent of angle Θ (degrees) or RΘ (Radians), numbered 5.73° to 84.28°. The standard "single scale" whereby the angles from 5.7 to 45 degrees being printed in increasing order (in black or blue), and angles between 84.3 and 45 degrees being printed in decreasing order (usually in red). When this arrangement is used, then tan(5.7) to tan(45) is read on the C or D scale (0.1 to 1.0), and tan(45) to tan(84.3) is read on the CI scale. Conversely, cot(45) to cot(84.3) is read on the CI scale (1.0 to 10.0) and cot(5.7) to cot(45) being read on the C scale.

T scale - On a commerce slide rule, the T scale is used for a relative date used for calculating the number of days between dates.

T (Greek letter tau) scale - Time constant= 1/ω, T=RC. [Pickett N16-ES Electronic slide rule]

T'C or X'C scale - On a Pickett N16-ES Electronic slide rule, these scales are used with scales at bottom and edge of right hand end plate (bridge) to determine decimal point location.

T1 scale - tan-1x, Tangent of angle T, numbered 5° to 45°. Also includes Cot T.

T1 scale - Used in some rules as the fundamental scale on the slide.

T2 scale - tan-1x, Tangent of angle T. numbered 41° to 85°. Also includes Cot T.

T2 scale - Used in some rules as the fundamental scale on the slide, folded at 360°.

Td scale - α/tanα, Tangent differential scale, for tangent range 0°to 60°. (PIC/Thornton)

Tachymeter Scale - A tachymeter (also tacheometer) scale is a logarithmic scale sometimes inscribed around the rim of an analog watch, useful in converting time intervals to speed or other rates of events, most commonly seen on chronometers. It can be used in auto rallyes and racing to compute a speed based on travel time or measure distance based on speed. It may also be configured on specialized watches to compute fuel reserve for aviator's or air reserve for divers.

Tachymeter Slide Rule - A Tachymeter slide rule has has additional trigonometric scales to be used for performing stadia calculations along with a theodilite, a surveying instrument used for the rapid determination of distances, elevations, and bearings. See the Faber-Castell 111/38.

Tamaya & Company - Tamaya & Company of Tokyo, Japan. Tamaya, a well-established and well-known firm in Japan, began selling Hemmi Slide Rules in 1913 and continued through 1932. There is some evidence that Tamaya licensed the Hemmi design for a time and sold to other companies in the UK (Stanley for example) as an OEM. Over 65 known model numbers may be found at Paul Ross's Hemmi Slide Rule Catalogue Raisonné Tamaya began as an importer of optical Surveying Instruments and Navigation Instruments prior to 1900 (Marine Sextant, Navigator Calculator, Binoculars, Clock, Barometer & Triangles) and later began manufacturing and distributing soley Japanese-made instruments. In the 1980's the company expanded into electronic calculators and the corporation was renamed Tamaya-Technics

Tavernier- Gravet - Late 19th century (c1820 - c1950) French slide rule manufacturer, Address: Rue Mayet 19, Paris, France. Began as the firm of Lenoir in Paris as skillful manufacturers of slide rules. Lenoir, then prominent in France for its excellent astronomical and geodetic instruments, gradually advanced until, for a time, it held the very first place in the world in the manufacture of slide rules. The most common Lenoir slide rule, before the Mannheim, was the Soho. There were two Lenoirs, father and son. The father outlived his son and died in 1832. The Lenoirs were succeeded by Collardeau and Gravet. According to Maurice d.Ocagne, the name of the firm was first Gravet-Lenoir, then Tavernier-Gravet. (Reference History of The Logarithmic Slide Rule by Cajori).

Technical Sales Ltd. - A British company in London that distributed Aristo slide rules and later re-branded Japanese slide rules with the TS logo, presumed to be manufactured by Uchida Yoko Company. Technical Sales Ltd was founded in 1948 to supply drawing and art materials to the retail, trade and education markets. Currently, the company specializes in leather portfolios for artists and photographers.

Technical Standard - A British brand of slide rules made by British Slide Rule Co. (per Peter Hopp,Slide Rules, Their History, Models and Makers p. 148). A Manual (owned by Jim Cerny) Lists these models: The Standard Rule (for general use), The Surveyor's Rule (for trig calculations and navigation), The Aeronautical Rule (for aeronautical and electrical engineers), The Pocket Precision Rule (with magnifying cursor), The Twenty Rule (with magnifying cursor), The Standard Pocket Rule (handy rule with 5" scales).

TECNOSTYL - An Italian manufacturer of slide rules (Calcolator) based in Segrate Milano, Italy. Founded in 1948, by Engineer Mayer (Majer) (Maeir) Berlin, since the time of its inception, TECNOSTYL has specialized in the production of high precision technical drawing aids and office products. The company is currently owned by the sons Gino and Guido Berlin.

Tehnolemn Timisoara - Romanian Manufacturer of slide rules during the Soviet Era. Although having to make slide rules under the GOST standards, they were made of higher quality than other Russian rules.

Teknilog - A Diwa (Denmark) and Deeva (India) model slide rule having 24 scales.

Teledyne Post - Teledyne purchased Post in 1970, and began changing the model numbers around in 1972. Probably a bad investment as the industry collapsed in the next few years. The Teledyne Post Versalog II was the preferred slide rule issued to U.S.A.F Academy cadets.

Tension Springs - Used to maintain tension on the slide within the stock of a slide rule in order to improve the feel and to keep position of the slide steady while manipulating the slide rule cursor. Closed-body slide rules had stocks that were split down the length of the stock and joined together with a thin metal or plastic insert that acted as a tension spring. Picket used a small flat spring in some of their all-metal rules to maintain tension. See Springy-Stocks.

Tertiary Divisions - Those graduations or tick marks on a scale that signify the third significant digit of a number. Tertially divisions are never labeled with their numeric value as the spacing is too small between graduations and must be interpolated by their position between the Primary divisions and Secondary divisions. See Sub-divisions.

Texas Speed Rule - A popular slide rule (Pickett model 905-ES) specifically targeted to students competing in UIL and Texas Competitive Mathametics slide rule competitions. The contestants had to complete a series of calculations in 30 minutes. As the competition was timed there was a premium on speed but the marking system also required high accuracy. If the answer was accurate to three place of decimals, three points were awarded but if the answer was off by more than 2 places in the third significant figure no marks were awarded. The Texas Speed Rule has two K scales, one of the stock and one on the slide, in order to facilitate cubes and cube roots faster. Complete Contest Sample (with answers) 196KB

Th scale - This is for the TANH (hyperbolic) function. Tanh = Θ(0.1 to 3).  Read Θ on Th and value of TANH Θ (0.1 to 1) on D. Angles in radians. Found on vector slide rules like the 1933 K&E 4093-3 Log Log Vector Duplex.

Theta or Θ - Angle in degrees. 0° to 90°.

Theodolite - A surveying instrument which resembles a small telescope, which is used for sighting lines and elevations in surveying. Also used in model rocketry for determining altitude or apogee of a flight. A Tachymeter Slide Rule was used in conjuction with theodilites for stadia calculations.

Tianjin Squirrel - A Chinese brand of all-plastic slide rule.

Thacher's Calculating Instrument - Patented in 1881 by Edwin Thacher. Originally made by W.F. Stanley, in London, but, by 1897, Keuffel & Esser had taken over production. an 1884 instruction book notes, "The original rule in use is 12 inches long, with radii of II and 5 1/2 inches, the divisions of which are cut by hand, copying from a machine divided plate. In the present instrument the radii are 60 and 30 feet, the divisions of which are printed directly from machine divided plates. Those plates contain over 33,000 divisions, calculated to seven places of decimals from Babbage's tables by using a common multiplier, every line being subjected to correction for error of screw and temperature variations, so that possibly every line center is within .0001 inch of its true place." The instrument consists of a cylindrical slide, which admits of both rotary and longitudinal movement within an open metallic framework of 20 equidistant triangular bars. The bars are connected to rings at their ends which admit rotation within standards attached to the base. Upon the slide are wrapped two complete logarithmic scales, each of which is divided into 40 parts of length equal to half that of the slide. The parts follow each other in regular order around the cylinder, and the figures and divisions which constitute any part of the right are repeated on the left, one line in advance. By the rotary and longitudinal movement of the slide any of its divisions may be brought opposite to or in contact with any division on the fixed scales. The divisions on the upper lines are transferred to the slide by means of a pointer fitting over the bars, which is also convenient for retaining the position of any division on either line while the slide is being revolved into the required position. Near the commencement of each scale on the slide is a heavy black mark designed to catch the eye.

Thacher, Edwin - (1839-1920) Edwin Thacher was born in De Kalb, Lawrence County, New York USA. His father was a doctor, but Edwin studied engineering at college. His first main job as an engineer was in 1864 as a military railway builder during the American Civil War. Later on he took up making bridges and worked for the Louis Bridge and Iron Company. A lot of his job as a bridge engineer involved doing mathematical calculations to work out how strong the steel girders and concrete beams in bridges needed to be. It was because he spent a lot of time doing calculations that he invented and patented (#249117) his cylindrical slide rule in 1881. He died in New York in 1920.

Things Of Science Club - From 1940 through 1989 the Science Service, founded in 1921 by journalist Edward W. Scripps and zoologist William Emerson Ritter. to inform the public of the latest scientific discoveries and achievements. They sponsored the Things of Science Club where. a limited number of subscribers received a monthly box containing some kind or material or artifact along with a pamphlet describing experiments that could be done with it. Sometimes the kits contained parts which could be assembled into a scientific instrument. There were three Math kits containing slide rules made by Engineering Instruments. A later kit had parts to build a slide rule.

Thomlinson's Equivalent Paper Slide Scale - made by J. Thomlinson Ltd, Glasgow, ca 1940. This specialized rule was designed for the paper and printing industry. The A scale indicated length, B scale the breadth, and area in square inches was read off the C scale. The D scale was used to read off translations of inches to centimeters, kilos to pounds, 480 and 500 sheet reams, and various weights of different standard paper cuts. Size: 8x58x1.5 cm. Brown, Wood, One Sided with Two Moving Rules.

Thornton, Alexander George - Founded the British company A.G. Thornton, in partnership with J. Halden. Thornton was trained by W.H. Harling, a company established in 1851. In 1890 Thornton established his own independent workshop and adjoining sales office in Manchester at 109 Deansgate. Acquired the Precision Instrument Company (P.I.C.) in 1900. PIC slide rule made by AG Thornton Ltd, Manchester, in about.1950.

Thornton, A.G., Ltd. - British manufacturer of slide rules, Drawing, surveying and scientific Instruments founded in 1878 by Alexander George Thornton in partnership with Joseph Halden. In 1890, after a falling out with the two partners, Thornton established his own independant workshop and adjoining sales office in Manchester. By 1895 the factory expanded to manufacture drawing instruments and in 1900 The Precison Instrument Company (P.I.C.) was acquired for their slide rules. The P.I.C. slide rules were made of mahogany and had framed-glass cursors and springy-stator floors. By 1925 the thornton line was described as the largest and broadest in the United Kingdom. A 1930's catalog lists more than 70 models carrying the P.I.C. brand name. In 1960 models of plastic were included in the product line and the firm renamed British Thornton. In 1980 it was sold and no longer produced slide rules. British Thornton merged with Education and Science Furniture (ESF) in January 1992 and moved to Burley, Wharfedale in Yorkshire.

TI scale - Two adjacent scales with a range of COT 45°-84.28° and TAN 45°-5.72° Found on the slide of the 1933 K&E 4093-3 Log Log Vector, which introduced decimal trig scales. Used in conjunction with their SI1 and SI2 scales. The stock has the standard T scale of 5.72°-45°.

Tomlinson, Henry W., Manufacturing - A manufacturing company in Chicago, IL that produced the Winslow Strength Computing Slide Rule Winslow, designed by Benjamin E. Winslow, a structural engineer/architect, which was used for calculating the loading on steel and wood beams. Two versions were made, copyrighted in 1904 and 1931. Other items by this company are unknown.

Tobe-Deutschmann, A US radio manufacturer, based in Canton, Massachusettes. This company was supplier of electronics parts to the U.S. military during World War two. Re-branded and sold Relay Slide Rules under the Tobe name, c1959.

Tongue and Groove - The feature used, in pairs, on on most every wood, metal or plastic slide rule that restrains the slide within the stock (stator). In some cases, such as injection molded plastic rules like late model Picketts, the grooves are on the slide and the tongue is on the stock, but most often, the slide will have the tongue, and the stock the groove, for ease of manufacturing. In some slide rules a small spring may be found within the tougue and groove to improve the feel of the slide and to prevent the slide from accidently slipping out of the slide rule.

Tower - Brand of slide rules sold by Sears and Roebuck that were made by Relay in Japan. Smith-Corona Typewriters were also re-branded with the Sears "Tower" brand.

Trademarks - Trademarks protect the manufacturers name and logos and model numbers and might include the colors or the "look" of the slide rule. In the USA registered trademarks are denoted by the symbol ® or TM. Parts of the slide rules and manuals may also be protected by copyrights ©.

Trig - A slide rule with scales for solving trigonometry problems. S, ST, T, etc.

Trigonometric Functions- are functions of an angle, important when studying triangles and modeling periodic phenomena. They may be defined as ratios of two sides of a right triangle containing the angle, or, more generally, as ratios of coordinates of points on the unit circle, or, more generally still, as infinite series, or equally generally, as solutions of certain differential equations. Example: SINΘ = OPP/HYP. COSΘ-ADJ/HYP, TANΘ=OPP/ADJ, etc.

Trigonometric Scales (S, T, ST, T2, P)- These scales are basically look-up tables for common trigonometric functions, usually marked in degrees, or in some cases degrees and minutes. Each scale relates to just one value on the corresponding base scale. The commonest set is probably ST, S and T, defined as arc(0.01x) (ST), arcsin(0.1x) (S) and arctan(0.1x) (T).

Troncet, J. Louis - A French inventor who created the Arithmographe, later know as the Addiator, in 1889.

Turbulent Flow Slide Rule - Designed to calculate the flow in pipes of liquids and gases. One was designed by C.F. Braun & Co, the Pickett Model 12, and another by the Service Pipe Line Company, the Pickett Model 7-T. Others may exist by other manufacturers.



U - Gauge mark converting degrees to radians 180/π=57.2958

U1 scale - Same as K, Cube scales in electrical calculations.

U2 scale - Same as A, Square scales in electrical calculations.

Uchida Yoko Co. - Founded by Kotaro Uchida in 1910 selling surveying equipment, drafting and office supplies. In 1925 the company enters into a domestic sales contract to market the Hemmi Bamboo Slide Rule which later becomes its flagship product. From 1926-1945, their Development Phase, Uchida Yoko's original products evolve into brand name items for which design is conducted in-house and production is outsourced. Numerous brand name products are launched including slide rules. From 1946-1962, what is called their Reconstruction Phase after WWII, Uchida Yoko begans utilizing the distributor network established for its flagship product, the slide rule, Uchida Yoko enters the school market by marketing science materials for the classroom. It is unknown exactly when slide rule production ceased, but the most likely year would be around 1975. They were a supplier of plastic slide rules to the Germany Company, Albert Nestler AG, which stopped production in 1972. Uchida Yoko Comapny Ltd continues to be a global manufacturer in Tokyo, Japan and one of Japan's leading companies in the school and educational market.

Unique - The British UNIQUE brand of slide rules was founded in 1920 by Burns Snodgrass (1886-1954) M.B.E, A.R.C.Sc., a mechanical engineering lecturer at Brighton Technical College. Unique specialized in a wide range of wood slide rules with celluloid covered paper scales and were most popular within the United Kingdom, and its colonies. The manufacturing process used fairly basic woodworking tools and printing presses, unlike their high end competitors which had mechanical tooling to make machine divided scales. This made possible relatively inexpensive slide rules that could also be customized to a broad spectrum of industries. The first Log Log slide rules were made around 1928-1929 and sold for 12 Shillings in 1931. Burns made these by himself on a part time basis until 1935, where he added a couple of employes, along with his son. In 1945, the last year of WWII, they sold 100,000 slide rules. In 1951 they became the Unique Slide Rule Company, Limited. Burns Snodgrass was also the author of Teach Yourself the Slide Rule ©1955 which was published in 1955, one year after his death. The book was popular for use in many schools and with other makers, although the graphics referred only to the UNIQUE brand. In 1954, The company was subsequently managed by his son, Donald Clayton Snodgrass. After an illness in 1981, Donald retired and his wife, Elain Snodgrass, took over as Managing Director. Various relatives worked in many aspects of the company making this a classic family business, much like all the other silde rule companies. It is estimated that they sold more slide rules in the UK more than any other maker, 2.5 million or more. In spite of their cheapness, older wood versions have survived in large numbers. They invested in all plastic slide rules in the early 1970's but found themselves, like other slide rule makers, obsoleted by the electronic calculator, and stopped production in 1975. They continued manufacturing other mathematical instruments as "Unique Instruments Limited" up until 1993 when Donald Snodgrass died..

Unique Five-Ten - A model of a slide rule made by the British firm Unique in Brighton, which combines the convenience of the 5-inch pocket size rule with the precision of the standard 10-inch rule. One one side the C and D scales are split into the C1, C2, D1 and D2 scales which are folded at 3.2. Similar to Charvoz-Roos SR-108 and Post 1442. The Unique Ten-Twenty utilizes the same principle, turning a 10-inch rule into the equivalent 20-inch rule.

Unique Ten-Twenty - A model of a slide rule made by the British firm Unique in Brighton, which improves the precision of the standard 10-inch rule to that of a 20-inch rule. One one side the C and D scales are split into the C1, C2, D1 and D2 scales which are folded at 3.2. See Unique Five-Ten. 

UNIS - Union Nationale Inter Syndacale. A French organization monitoring the quality of French goods. The "UNIS" marking found on slide rules was more or less equivalent to stating that the product was "Made in France".

United Kingdom of Slide Rule Collectors (UKSRC) - The UKSRC was formed in the mid 1990's as an informal group of slide rule enthusiasts with the aim of providing a forum for discussion and contact between members. In 1998 the publication of the newsletter Skid Stick was started, followed by the annual Gazette in 2000. The UKSRC has found it preferable to retain its informal and friendly atmosphere and has no elected officers, various functions being carried out on a voluntary basis. The UKSRC aims to hold "local meetings" two times per year. These normally take place at a member's home and provide an opportunity for personal contact, exchange of views and information, and for the discussion of proposals for the advancement of our interests. Since 1995 International Meetings have been held annually, the venues having rotated every three years between Holland, Germany and England (plus one in Switzerland) reflecting the co-operation between the various national groups. More

University Interscholastic League - The UIL An extension of The University of Texas founded in 1909, that held slide rule competitions. From their web page: "The purpose of the UIL is to organize and properly supervise contests that assist in preparing students for citizenship. It aims to provide healthy, character building, educational activities carried out under rules providing for good sportsmanship and fair play for all participants." Up until 1980, when the calculator replaced the slide rule, competitions were held for "Slide Rule and Number Sense". See UIL Results from 1945-1980. Modern speed contests using calculators are currently held by the Texas Competitive Mathematics.
Complete Contest Sample (with answers) 196KB

U.S. Air Force Academy - The USAFA, located north of Colorado Springs, Colorado, was begun in 1958. Incoming cadets (doolies) were issued slide rules. From 1959-1966 they were given Post (Japanese Sun Hemmi) slide rules, then from 1967 through 1969 they were issued US made K&E 4081's. The stitching on the sleeves was not as good as Post's so the switch to the Post Versalog started in 1970 and continued through 1975. During the later period, in 1972, cadets with engineering majors began transitioning, at their own expense to the HP 35 electronic calculator ($375). In 1975 the dean of the school officially made the change from analog to digital and began issuing Texas Instruments SR-51 electronic slide rules for future classes, taking up an entire two-week production run at the TI dallas plant. A display of math instruments used by USAFA cadets currently hangs in the campus.

    Chronology of Math Instruments used by USAFA Cadet classes:
  • Classes of '59-'66 - Post Versalog 1460 Slide Rule
  • Classes of '67-'69 - K&E Decilon 68-1100 Slide Rule
  • Classes of '70-'78 - Post Versalog II 1460 Slide Rule
    Engineering Cadets allowed to own HP-35 at their own cost, but the slide rule must be used for exams.
  • Classes of '79 - Texas Instruments SR-51 Electronic Slide Rule
  • Classes of '80 - Texas Instruments SR-51A Electronic Slide Rule
  • Classes of '81-'83 - Texas Instruments SR-51-II Electronic Slide Rule
  • Classes of '84-'85 - Texas Instruments TI-55 Scientific Calculator
  • Classes of '86-'87 - Texas Instruments TI-58C Programmable Calculator
  • Classes of '88-'90 - Texas Instruments TI-66 Programmable Calculator
  • Current classes - Texas Instruments TI-30XIIS, a 2-line scientific calculator
    called the "Honorator" because it can't store answers in memory like a programmable.

USAF Test Pilot School - The Test Pilot School is located in Edwards AFB in California, this school's patch is a Jet fighter with a slide rule on its crest. The Air Force Flight Test Center is the free world's largest aircraft test facility. Nearly every aircraft used by the Air Force over the past four decades has been tested and developed at Edwards. This is where many of the Astronauts are chosen.

U.S. Military Academy - The USMA at West Point, located 50 miles north of New York City, NY began using slide rules in 1929 as a formal part of the mathematics program, for surveying, ordanance and gunnery, and they served as the midshipmen's primary calculator until 1976. A 1934 Information to cadets states At the beginning of Academic work on September 1 and for about two weeks thereafter, a portion of each period of instruction is devoted to the use of the slide rule, and thereafter proper use of the slide rule for computations in the department is obligatory. Cadet pay back in 1957 was $111.15 per month, with the bulk of it placed into a "fixed" account for uniforms, books, slide rules, and such, while the remainder was placed into a "regular" account for discretionary expenditures. Keuffel & Esser is the maker of all slide rules used at the USMA. In the fifties the K&E 4018-3 Decitrig was issued followed by the K&E Decilon 68-1100 during the 1970's. TI-55 Electronic Slide Rules was issued in 1980.

U.S. Naval Academy - Annapolis, MD. Cadets in the U.S. Naval Academy, were issues different slide rules over time. During and immediately after WWII, at least up through 1950 the K&E Log Log Duplex Trig slide rule was issued. It was prefered over the decitrig and vectors models because of the need to solve navigation problems. Navy pilots used the E6-B in the cockpit. ref: Earl K. Dille of the ISRG If the officer had graduated from the Naval Academy in the early '70s the rule issued to him would have been a Pickett N803ES and/or a Pickett N600ES. These were the standard issue rules at that time. ref: Jim Beaver LCDR USN (ret.). The USNA currently issues Texas Instruments Voyage 200 Electronic Calculators to incoming freshmen.

UTO - Fabrikken UTO out of Vonge, Denmark founded by Kal Kruuse and Poel Larsen after breaking away from DIWA, in 1957, a 16 year partnership. Kruuse and larsen had invented a logarithmic dividing (engraving) machine which had prompted DIWA to hire them in 1941. The UTO chracters do not stand for anything, but were chosen because this name could be pronounced very easily in America as well as in Japan. Hoffman, presumed to be a German distributor, appears on many of the model UTO 601 pocket slide rules. UTO slide rules are still made to this day. "The UTO SR's made now are silk screen printed on hard white PVC sheets, 7 - 9 bodies on a sheet, and machined to final shape. The cursors are injection molded of acrylic. The grooves for sliding the cursor are positioned to prevent the cursor to touch the SR surface. The printing ink bonds chemically to the PVC surface." Courtesy of John Kvint, of UTO. UTO board of Directors Poel Larsen, Kal Kruuse,and Hans Jorgenson can be seen in this Danish newspaper article and the ladies in the UTO Factory Floor. courtesy of IJ Schuitema.



V or ς- Gauge mark denoting radian equivalent to small degrees π/180=0.1745

V-line A gauge mark for finding the volume of a sphere (V=d²π/6) when its diameter is known. Found on Chinese slide rules like the Shanghai Flying Fish. The V-line is engraved on the K scales between the numbers 520 and 530, equal to π/6 = .524. Using the hairline, set the right index of the C scale on the V-line and for any diameter on the C scale, the Area may be found above on the K scale.

V scale - Volts, for electrical calculations.

Vd scale - Volt Drop, On Electro slide rules for voltage drop in conductors.

VEB EAW - VEB Elektro-Apparate-Werke, Berlin-Treptow, GDR, was a socially owned industrial holding, founded in 1928 in Berlin, Germany which was located on the German Democratic Republic side of Berlin after WWII. Friedrich Ebert was master of the operation VEB Elektro-Apparate-Werke (K VEB EAR) and with over 8,000 employees was one of the largest manufacturers of electric appliances in the GDR. The company produced radios, relays and control equipment, circuit breakers, vacuum contactors, rectifiers and computers, as well as one known slide rule.

VEB Mantissa - Volks Eigens Betrieb. An East German manufacturer of plastic slide rules that was located in Dresden, Germany. Founded in 1932 by P. Lübker, as Lübker & Co. and produced a low quality Rietz(mode 72/2) and Lübkernorm slide rule out of beechwood. In 1947 the firm went bankrupt and was taken over by one of its workers, Horst Meissner. Now named Meissner KG, Precision Instrument Factory, Rietz and Darmstadt beechwood slide rules were sold mainly in Eastern Europe, and some to Western Europe. The double sided Darmstadt-Record was popular model. In 1972 the firm was nationalized by the east German government (DDR) and renamed VEB Mantissa, retaining "Meissner" as a trademark. Specialty slide rules were produced as well as models for the Warsaw pact artillery. VEB continued to make slide rules and supply schools with the Mono-Rietz until 1984.

Vector Slide Rule - A slide rule with hyperbolic functions  Sh, Th, etc.

Veneer - Thin strips of material applied to a thicker substrate, or used together in a composite construction to increase the strength of wood and to reduce warpage. In the case of slide rules, veneers of celluloid were laminated onto stocks starting in 1886 by Dennert & Pape, in order to improve the readability of the scales. Veneers were glued and positioned with small posts and screws. Over time, many such veneers had shrunk faster than the corresponding wooded stocks and slides, but as long as the veneers shrunk together it did not affect the usefulness of the slide rule since the scales are comparative. Mahogany and Bamboo proved to be popular materials for matching the shrink characteristics of celluloid.

Vero, J. (or Verie) - A British excise examiner that introduced the C & D (1-10) scales to compliment the A & B (1-10-100) scales, prior to 1778.

Versalog - A popular model amongst engineers of a complex duplex slide rule sold in the U.S. made specifically for the Frederick Post Company and manufactured by Hemmi with the Post brand. Jointly developed in 1951, the pocket version, 1461, appeared in 1957. It has multiple log scales. The Post Versalog 1460 and later the Versalog II was issued to all U.S. Air Force Academy cadets in Colorado Springs, Colorado, up until the mid-70's. Teledyne relabeled the model number to 44DA-410. The Sun Hemmi brand was labeled #258 and Hughes-Owens (Canada) labeled theirs as 1777. They all use Hemmi date codes. About 600,000 Versalogs were manufactured.

Versatrig - A Post model of a duplex slide rule have primarily trigonometry related scales. Introduced in 1951 as the Post 1450. The pocket version appeared in 1957. This slide rule is of the same generation as the popular Versalog (Post 1460/1461).

Vinyl - A white plastic used in the 1960's to make stocks and slides for slide rules, such as the Acu-Math models 150, 600 and 900 of 1961.

Vinyl/Magnesium - A laminated white plastic over a magnesium substrate used in the 1960's to make stocks and slides for slide rules, specifically by Acu-Math for their higher-end models 511, 1211 and 1311 of 1961.

Vittorio Martini - Antica Fabbrica (Ancient Factory) Vittorio Martini, Bologna, Italy. Company founded in 1866 by Cavalier Vittorio Martini. Made plastic slide rules "regolo calcolatore" in the 1960-1970's. and continues to produce technical articles for design, precision instruments for calculation and measurement for engineering, architecture and nautical. Current Company Website (Italian).

Volt scale - A scale for calculating Voltage Loss, numbered 0.5 to 10. Often found in well of stock.

Vulgar Fractions - A fraction in which both the numerator and denominator are integers, such as: ¼, ½, ¾, etc. Also known as Common Fractions. Excludes decimals and denominators with a radical component such as: 1/√3.



W - Gauge mark denoting weight of copper conductors W² = 111000. This point, along with R, were used regularly by electrical specialists.

W - Gauge mark denoting watts in one horsepower (HP) at 745.47

W1, W1', W2 and W2' scales - These are two pairs of double-length scales that cover half the range of 1 to 10. They are placed on the back side of a duplex rule where A,B, C and D would normally be found and used together to perform multiplication with greater precision ( a longer scale makes it easier to align the numbers and read the answer). Found on a Faber-Castell 2/83N.

W&G - W&G Record Processing Company. White & Gillespie, Melbourne, Australia, was founded in 1910, as a manufacturer of printing plates and specialist printer equipment suppliers (and continues to the present day)and in 1938 White & Gillespie created a separate wholly owned subsidiary, called the W & G Record Processing Company. Its initial purpose was to make radio transcription records. At the commencement of WWII in 1939 W&G became involved with the Australian War effort and began producing navigational aids and range finding devices and slide rules for artillery. After WWII, W&G continued to produced slide rules, drafting aids and navigation equipment and LP record pressing equipment, up to 1977, when the firm was sold.

Watkins & Hill - The English firm Watkins & Hill, Charing Cross, London was started in London in the first half of the eighteenth century under the name of Watkins. The name of William Hill was added c. 1805. Watkins & Hill made and sold a variety of scientific instruments including telescopes, air pumps, electrical demonstration apparatuses, and mathematical instruments. Watkins and Hill were taken over by Elliott Bros in 1856, both partners having died by 1847. and the firm having been continued by Armistice Day 1918.

Walther, Dr. Alwin - (1898-1967) In 1935, Dr. Walther, of the Institute for Applied Mathematics, Technical University, Darmstadt, proposed an arrangement of scales which became known as Darmstadt. System Darmstadt slide rules were probably the last standardized arrangement to be accepted.

Weber, Frederick. - (? - 1919) Original owner of the F. Weber & Co. located in in Philadelphia, PA. F. Weber was originally founded as Scholz and Company, a sales agency, in 1853, became Janentzky & Weber in the 1880's and  renamed F. Weber & Company in 1887. Frederick Weber was survived by his two sons Frederick (Fred) and Ernest who incorporated the the firm after his death in 1919.

Warner, John - (c1682-c1705) Apprenticed to Henry Wynne of the Clockmakers' Company on March 29,1675 and was free of the Company on April 3, 1682. He took apprentices and became an instrument maker, including barometers and slide rules. In 1722 made improvements to the type of slide rule which he manufactured by introducing square and cube scales.

Weber, F., & Co. - F. Weber & Co. (1853-present) originally began as Scholz and Company, a sales agency, in 1853. In the 1880's  a partnership was formed as Janentzky & Weber. In 1887 the firm was renamed F. Weber & Company by its sole owner Frederick Weber. F. Weber & Co.located at 1125 Chestnut Street in Philadelphia, specialized in the importation and manufacture of artist and drawing supplies, importation of Draughtsman tools from C. Riefler (Germany) and slide rules from Albert Nestler (Germany). After WWI customers preferred American made products and F. Weber began manufacturing some of its own products. Frederick Weber was survived by his two sons Frederick (Fred) and Ernest who incorporated the the firm in 1919. By 1920 there were retail stores in St. Louis, MO, Baltimore, MD and Philadelphia, PA. A pre-WWII domestic supplier was Charvoz-Roos. Purchased in 1980 by the Kapp family and currently named Martin/F.Weber which sponsors the well known TV artist Bob Ross. More details at Martin/F.Weber Co.

Welch, W. M. - W. M. Welch Mfg. Co. Chicago, Illinois was  established in 1880  by W. M. Welch (1856-1940). Name changed to Welch Scientific Company in 1930 and located at 1516 Orleans Street, Chicago, Illinois. Specialized in Scientific Instruments, Laboratory Apparatus and Supplies for Physics, Chemistry and General Science.  Made a four foot  teaching slide rule for hanging in classrooms Size: 2x23x125 cm. One sided, black background with four white scales, out of Masonite, with Hangers. W. M. Welch later became part of Sargent-Welch Scientific Co. Pumps were spun off and became Gardner Denver Welch Vacuum Technology. Medard W. Welch, son of W.M. Welch, was an original founder the American Vacuum Society in 1953.

Well - The channel or gap in a closed body solid framed slide rule above which the slide moves. additional scales can sometimes be found in the well to lengthen linear scales or for electrical calculations.

W.H. Smith - A British retail company that sold rebranded slide rules of British manufacture. The W H Smith rules were based on the Blundell Harling Ltd. rules current at the time including 800 series rules, S prefixed rules and the Super Duplex A505.

Wichmann, Gerbil - A German Manufacturer, located in Berlin, was founded in 1872 as a mail order house of drafting instruments. Wichmann slide rules had a simple A[B,C]D scale set, made with a printed laminate over a paper composite. A one piece chisel cursor was used. The Wichmann logo was a "frontiersman with rifle over shoulder". Two known models are the 12.5cm #441 and 25cm #431.

Wingate, Edmund - Credited with independently duplicating Oughtred's work around 1630.

Winslow, Benjamin E. - A structural engineer/architect that designed the Winslow Strength Computing Slide Rule used for calculating the loading on steel and wood beams. Two versions were produced by Henry W. Tomlinson manufacturing, Chicago, IL, copyrighted in 1904 and 1931.

Wood - Used to make the Body (Stock or Stator) and Slide of most slide rules prior to 1960. Popular woods were Bamboo, Mahogany, Rosewood, Basswood, Beechwood, Magnolia, Swiss Pearwood, Mongolian Ash and Boxwood. Wood slide rules were initially engraved or printed directly on finished wood, but by 1900 most quality slide rule manufacturers were engraving the scales on celluloid laminated wood.

Wollaston, William Hyde - (1766-1828) An English chemist, was a pioneer of powder metallurgy and discovered rhodium and palladium. He developed the Wollaston Chemical slide rule, c1820) to enable calculations of chemical proportions (relative weight of reactants), using a logarithmic scale of chemical equivalents. Like most early 19th century chemists, Wollaston used equivalents rather than atomic weights in an attempt to avoid the various problems associated with the latter. Compounds and elements are marked on the outer scale. The slide rule was made of boxwood by Dring and Fage of Tooley Street, London.

World's Slide Rule Records
20 feet long overall weighing 110 lbs. constructed in 1973-74 by Ralph Nyberg and members of the Mathematics Club of Roanoke-Benson High School, Illinois. Guiness Book of World Records, 1976, Sterling Publishing Co, New York, NY USA.
59 feet 1 1/4 inches in length designed by Ralph J. Snelson and R. Clayton Brough and built by students at Springville Junior High School, Springville, Utah. Guiness Book of World Records, 1978, Sterling Publishing Co, New York, NY USA.
320 feet 11.1 inches in length completed in March, 1979, by students of Alvirne High School, Hudson, New Hampshire. Guiness Book of World Records, 1980, Sterling Publishing Co, New York, NY USA.
323 feet 9.5 inches in length completed on Nov 11, 1979 by Greg Maggs and Robert Kolstad at the University of Illinois College of Law Building in Champaign, Ill. Guiness Book of World Records, 1983, Sterling Publishing Co, New York, NY USA.
350 feet 6.6 inches and currently the World's Longest documented Slide Rule, The Texas Magnum by Skip Solberg and Jay Francis,was demonstrated on February 28, 2001 in the Lockeed-Martin Aircraft Assembly Facility at Air Force Plant 4 in Fort Worth, Texas. The Texas Magnum is holds the world's record for the longest linear slide rule. The Texas Magnum was designed as a traditional Mannheim style slide rule. The A, C, D and L scales are included on the slide rule.

WWI - World War I (1914-1918).

WWII - World War II (1940-1945).




x - the variable or principle number on the C or D scale. If on C then Y is on D.

X'C or T'C scale - On a Pickett N16-ES Electronic slide rule, these scales are used with scales at bottom and edge of right hand end plate (bridge) to determine decimal point location.

X* scale - Used in conjunction with the C and D scales to keep track of the decimal place in a result. Found on some Pickett slide rules replacing the A scale and ranges from -10 to 0 to +10. See Decimal keeper and Decimal Tracking

XC scale - Capacitive reactive impedance in ohms [Pickett N16-ES Electronic slide rule].

XL scale - Inductive reactive impedance in ohms. * Row of dots directly above XL scale are standard resistance values (in ohms) when referred to XL scale [Pickett N16-ES Electronic slide rule].

Xylonite - Keuffel & Esser's brand name for the celluloid plastic they used to laminate their wood slide rules.




y - the variable or secondary number on the C or D scale. If on C then x is on D.

Y* scale - Used in conjunction with the C and D scales to keep track of the decimal place in a result. Found on some Pickett slide rules replacing the A scale and ranges from -10 to 0 to +10. See D*, X*, Decimal keeper and Decimal Tracking




Z scale - Interest rate calculations, numbered 10 to 0. Small scale on stock (PIC/Thornton)

ZS scale - Surge impedance of transmission or characteristic impedance in ohms [Pickett N16-ES Electronic slide rule].

Zulaica y Cia - A firearms company founded by Bruce M. Zulaica, in Eibar, Spain. They made a pocket slide rule of sheet metal, called Stilus, marked as being made in Zarauz, Guipuzcoa the Basque region of Spain. They started out business in the early 1900s manufacturing small inexpensive 'Velo-Dog' (velocipede - dog) type folding trigger pocket revolvers that were designed for use by bicyclists as protection against dog attacks. In 1905, Zulaica patented a design for an automatic revolver but few were ever manufactured and even fewer have survived. In 1915 Zulaica started manufacturing 'Eibar' type semi-automatic pistols for WWI French military contracts. After the war, the Eibar pistols were sold on the civilian market into the 1920s. Zulaica's last design which was introduced in about 1930, was a copy of the C96 Mauser. Marc Note: Cia is short for Compania or in english, Company)

ZZ1 scale - Same as LL1 scale or  e0.01x. On financial scales this is used for compound interest factors.

ZZ2 scale -Same as LL2 scale or e0.1x. On financial scales this is used for compound interest factors.

ZZ3 scale - Same as LL3 scale or ex. On financial scales this is used for compound interest factors.

Modern Translation: Slide Rule

Language Translations for Slide rule,
Sliding rule, Slipstick, Calculating Ruler


rigë llogaritëse


‏مسطرة حاسبة, ‏المسطرة المنزلقة.


логаритмична линийка


logaritmické pravítko.


skydelaere, regnestok


schuifmaat, rekenschuif, rekenliniaal, rekenlat




règle àà calcul.


Rechenscheibe, Rechenschieber, Rechenstab


κανόνας υπολογισμού, λογαριθμικόσ κανόνασ, λογαριθμικός κανόνας


קררע, סרקל חשוב.






regolo calcolatore

Japanese Kanji 

計算尺 , 滑り尺 .  

Japanese Katakana 

すべりじゃく, けいさアじゃく.  


regnestav, regneskive


régua de cálculo


riglã de calcul


логарифмическая линейка,
Счётная линейка


tehnička računaljka, iber.


regla de calculo


räknelinjal, räknesticka


sürgülü hesap cetveli, hesap cetveli


логаріфмічна лінійка

Bibliography and Acknowledgements

Information presented on this page is an accumulation of personal facts and knowledge using reference material on the web, slide rule manuals and books related to slide rules within the public domain. My apologies to anyone if it appears I have inadvertently plagiarized their work or not recognized them in this Bibliography.
  • History of the Logarithmic Slide Rule by Florian Cajori, School of Engineering, Colorado College, 1909, OCR Facsimile courtesy of Ron Manley's
  • Slide Rules, Their History, Models, and Makers by Peter M. Hopp, C.Eng. MBCS. (1999) Astragal Press
  • Slide Rules, A Journey Through Three Centuries by Dieter von Jezierski, (1997), Translated by Rodger Shepard, M.D. M.P.H. (2000) Astragal Press
  • Calculating on Slide Rule and Disc by Ir. Ijzebrand Schuitema and Ir. Herman Van Herwijnen (2000) Astragal Press
  • Slide Rule, A practical Guide to its Use with Examples, Problems, Answers - College Outline Series by Calvin Bishop (1947); Barnes and Noble (1955)
  • A Course In The Slide Rule and Logarithms - E. Justin Hills; (1938) revised: Ginn and Company Publishers (1950)
  • Newnes Slide-Rule Manual - by F.J. Camm (1948) ; Geo. Newnes Limited, London, England.
  • The Slide Rule and Its Use - by Sommers, Drell, Wallschlaeger (1942); Grosset and Dunlap, New York.
  • Thornton PIC Slide Rules, Instructions for use - 1962 A.G. Thornton Ltd, Manchester, England.
  • The Oughtred Society, including the web site, The Journal of the Oughtred Society (JOS) and its many worldwide members
  • The United Kingdom Slide Rule Circle, including the web site, Skidstick and its many worldwide members
  • Ron Manley's Slide Rule Site
  • Clark McCoy's K&E Catalog Site
  • Sphere Research Slide Rule Learning site (Canada)
  • Slide Rule Archive Site by D.Davis
  • Thanks to John Mosand in Norway for providing translations and editing.
  • Thanks to Cyril Catt in Australia for research and editing.
  • Thanks to Paul Hilrose in the USA for corrections.
  • Slide Rule Accuracy vs. Precision essay (.pdf file) by Alan Morris, Dr.Eng., P.E. Version, 8/10/99
  • Japanese Slide Rules - William Lise(Japan)
  • Greg's Slide Rules - Greg Scott (Australia)
  • Slide Rules, How they work - John Savard (Canada)
  • About Slide Rules - Nigel Bromley
  • Peggy A. Kidwell, Curator of Mathematics, Smithsonian Institution
  • ®
  • MacTutor History of Mathematics Archive - University of St. Andrews, Scotland
  • Christian Hamman On-Line Museum - Technische Fachhochschule Berlin University of Applied Sciences, Germany
  • Mathematical Iinstruments - A Private Collection of David M. Riches. England.
  • The Slide Rule Technical Cultural Heritage,by IJzebrand Schuitema, 2001)
  • Tom Dilatush's Collection of Mechanical Computing Devices
  • Thanks to Richard Davis in the USA for historical contributions.
  • Thanks to Jürgen Nestler in Germany for historical information and images on his family concerning Nestler Slide Rules.
  • Thanks to David Rance in the Netherlands for historical information on European Slide Rules.

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