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Circular Slide Rules and selected Disk Charts


KEEP ISRM FREE!
This gallery has a wide variety of circular slide rules and many of these images may be duplicated on their respective manufacturer or country galleries. The well-known Gilson Binaries/Atlas, the Concise line of products, and Aristo, Faber-Castell, and Pickettcircular slide rules have been moved to those respective galleries, along with Controller, Norma and Standardgraph into the Germany/DDR gallery. Specialized/promotional cardboard/plastic film circular slide rule/calculators are also found at the Slide Charts Gallery. The advantage of circular slide rules, is that the dimensions can be small enough to fit in your shirt pocket, yet have the scale resolution of a standard linear slide rule. Construction is simple as the only only fastener is the single screw or rivet at the center of the disk. A few Disk Charts are ahown which logarithmic scales or of unusual construction.

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?'.


For Pocket Watch styles, visit the Pocket Watch Gallery

For Aviation/Airborne related styles, visit the Aerospace Gallery

For Artillery styles and Government Issued slide rules, visit the Military Gallery
Manufacturers found in this gallery (in no particular order), Alro, Dempster, Boykin, Huet, Amphenol, Miller Dial, C-Thru, General Electric, Martin Company, Layne (Thomas Sheahan designs), G. Felsenthal & sons, General Luminescant Corp, Cruver Manufacturing Co., J.B. Carroll Company, Weems System, Weems & Plath, American Airlines, Jeppsen, Whitehead, Aero Products Research, Science Spectrum Inc., White & Gillespie, American Hydromath Company, T&T Calculator, Associated Spring Corp, Standardgraph, Gilson, Compass, Dietzgen, Pickett, Aristo, faber-Castell, Lietz, SIC, Scientific Instruments, Concise, Sama&Etani, Lafayette, US Army Signal Corps, Cox, Hemmi, Norton & Gregory, Controller Calculator, Mascot, Circhlow, Emeloid Operations, Graphic Calculator Co., Ahrend, Waltham, Educational Instruments, Inc., Chadwick, Gong Se He Ying.



OAO Kalibr Moscow Circular Slide Rule Calculator

REF
OAO Kalibr Moscow Circular Slide Rule Calculator
Made in USSR by OAO Kalibr-Moscow
Front Scale (with logo)
K, A, C ( D, CI )
Back Scale: T, ST, S ( C, L )
Photo Contributed By Dushan Grujich Collection, Australia


ALRO PATENT System ALRO 200R

ISRM 13.01.26.01
ALRO PATENT System ALRO 200R
Made in The Hague, Holland
Dimensions: 125x135x12 mm
Patents No's (stamped on metal hub): USA 2,117,155; France 808,295; Gr. Britain 443689; Belgium 413,897; Germany 643,571; Holland 41,324
Front Scale
S, T, S&T, kW, N2, N ( N , N2, R, N3)
Cover Scale: Decimal/fraction, Log spiral scale
Acquired from the Netherlands, made possible by a gift from Robert L. Allison of Ballard, Washington.
See many more specimens in the ALRO gallery here at ISRM.


Dempster RotaRule - model AA (Dietzgen 1798 w/Case)

ISRM 13.05.28.01


Instruction Sheet, Legal size, two front and back sheets
Dempster RotaRule - Model AA (1933-1948)
Made in USA - Designed and manufactured by Jack Dempster, Berkeley, California.
Front Scales: K, A, D ( C, CI, CIF, S, CS, ST, T, CT, G, B, F/i )
Back Scales: 1-100 in 4circles, DLL, V2 ( V1, 1-100 in 4circles, LL3, LL2, LL1, LL%, L )
Acquisition made possible by contributions from Dick Rose Vintage Instruments

Dietzgen Model 1798C leather case, Model 1798 shown in 1938 Dietzgen Catalog (in ISRM Library), additional image from Hermann's Slide Rule Catalog as ISRM specimen has a faded back cursor.



REF - Boykin RotaRule - model 510

REF
Boykin RotaRule - Model 510 (1960-1973)
Made in USA - Designed by Bernard C. Boykin (1921-2011), Ruxton, Maryland.
Front Scales: K, A, D ( C, CI, CIF, S, CS, ST, T, CT, B, L )
Back Scales: D50:1-100 in 4 circles, DLL (V2, V1 C50:1-100 in 4 circles, LL3, LL2, LL1, LL01, LL02, L03 )
Archive - Various sources

Bernard C. Boykin passed away May 12, 2011. He was 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. After the war he designed the Boykin RotaRule, a very complex disk slide rule used by engineers and scientists for their calculations. It was based on the Dempster's Rotarule design who's patent had expired, but with improved scales. The trig scales are in decimal degrees.


Huet MG 240C Circular

REF
Huet MG 240C Circular
Made in France - 1925br> Front Scale (Long Spiral): Sines, Tangents, Metres
Archive - Courtesy of Rod Lovette's Collection (UK)


Amphenol Circular Slide Rule & RF Smith Chart

ISRM 13.02.13.05

Note: Bunker Ramo Corporation was founded by George M. Bunker and Simon Ramo in 1964, jointly owned by Martin-Marietta and Thompson Ramo Wooldridge TRW. The resulting company, Bunker-Ramo, was based in Trumbull, Connecticut.It became a manufacturer of military electronics devices and digital computers. In 1967 the Amphenol corporation (a manufacturer of electrical connectors) merged with Bunker Ramo.
Amphenol Circular Slide Rule & RF Smith Chart
Made in USA by Bunker Ramo, Amphenol RF Division, Danbury, Connecticutt.
9.25in [23.5cm] Diameter Plastic Film
Front Scale: D, ( C, CI,A, K, L, T Cot, S Cos, ST)
Back: Radio Frequency Smith Chart (with cursor on cursor):
Wavelength toward Generator, Wavelength toward Load (Angle of Reflection, Negative Reactance Component, Positive Reactance Component, Resistance Component)
Cursor Scales: Voltage or Current Limits, Voltage or Current Ratio, Attenuation Dissipation Reflection, IDB Loss, Toward Generator, Toward Load
Detail of Sliding Cursor mounted on Rotating Cursor on Smith Chart Side.
This slide rule and others in the ISRM archives were donated through the generosity of Phillip Rodley of New Zealand


Science Spectrum Octal-Decimal Slide Rule Calculator

REF
Science Spectrum Octal-Decimal Slide Rule Calculator 1969
Made in USA by Science Spectrum, Inc, Santa Barbara, Calif.
Designed by Phillp J. Wyatt, Albert S. Trundle, Judith B. Bruckner
Patent Filed in 1969: Issued April 4, 1972, US 3,654,437
8in Diameter Vinyl Plastic disk.
Note: This design is similar to the single Gilson circular slide rule with three cursor arms.
Back Scale: (Octal: CO, C20) (Decimal: D spiral scale)
Archive - Photo by David Sweetman collection, Nevada

Company Logo, 1969 Sales Brochures (236 Kb PDF), 1972 Patent (1MB PDF)


Science Spectrum Hexa-Decimal Slide Rule Calculator

REF
Science Spectrum Hexa-Decimal Slide Rule Calculator 1969
Made in USA by Science Spectrum, Inc, Santa Barbara, Calif.
Designed by Phillp J. Wyatt, Albert S. Trundle, Judith B. Bruckner
Patent Issued 1972, Filed in 1969: US 3,654,438
8in Diameter Vinyl Plastic disk.
Note: This design is similar to the single Gilson circular slide rule with three cursor arms.
Front Scale: (Octal: CH, CIH, AH, LH) (Decimal:C, CI A, L ) ( 16H: Decimal Powers of 10H(=16D) Scale)
Back Scale: (Octal: CH ) (Decimal: D spiral scale)
Archive - Photo by David Sweetman collection, Nevada

Company logo, 1969 Sales Brochures (236 Kb PDF), 1972 Patent (1Mb PDF)


Curtis L-M Rule, Frequency Response Calculator 1953

ISRM 14.04.30.01

The above circular slide rule belonged to Ben Emmerich (1922-2010). He was a German aircraft engineer who in the course of his career helped develop the Transall, the Starfighter, the Tornado and the Eurofighter. The slide rule was donated in his memory by his family.
Curtis L-M , Frequency Response Calculator
Made in USA. Designed by Emory C. Curtis ©1953.
Construction: 6-1/4 in Diameter Disks. 3 plastic disk with paper scales.
Front Scale: Frequency, Frequencing Ratio, Damping Ratio (Xm/Xo, Phase Angle Degrees)
Back Scale: Decibels, Aplitude Ratio, Damping Ratio, (Mp, Amplitude Deviation, Formulae)
Gift of Ellen Emmerich, Munich, Germany, in memory of her father Ben Emmerich.
Ellen Emmerich, his daughter, writes: "A friend of my father's in Minneapolis says: 'The slide rule you have is used to calculate the frequency response of control systems. Your Dad might have used it in his work on the VJ101. The graph on the bottom view is a Bode plot of a second order system. The slide rule would allow you to enter the damping ratio of the system and the trequency with which the system was being driven; and it woult tell you the ratio of the system output to its input. Examples of second order systems would be a spring suspended from a coiled spring. Another would be the servo actuators we used on the VJ101 to position the engine throttles.'"


Fearns A7 Universal Metric Converter

ISRM 17.10.10.04

Instructions
Fearns A7 Universal Metric Converter
Made in England by Fearnes Calculators, Dunston, Gateshead 11, UK
5-1/2 in Diameter Pasltic
Front Scale: Index (1-105), Metric (C) (Imperial (D)) &dec;F, °C
Back: Instructions, Conversion Index, Abbreviations, S.I. Units, Notes
Original Owner/Location: Brian C. Cunningham, Australia (has name on back of stock)
Donated by Andrew (son) and Barbara (wife) Cunningham, Willagee, W.A., Australia.

Brian C. Cunningham (1935-2013)
Brian was born in Port Pine, South Australia, Australia. His education commenced there and continued at the South Australian School of Mines where he gained his Diploma in Mining & Metallurgy. He became a Student Member of the Australian Institute of Mining & Metallurgy rising to a Fellow member. Brian started his career as a Metallurgical Cadet at the B.H.A.S. (Broken Hill Associated Smelters) in Port Pirie. He transferred to Hamersley Iron in Perth, Western Australia, the subsidiary company of Conzinc Rio Tinto Aus. where he became an Executive Officer of the Hamersley Iron Group. In Brian's studies and work his slide rules where used extensively.


Fearns A13 Circular Slide Rule

REF

Fearns A13 Circular Slide Rule
Made in England by Fearnes Calculators, Dunston, Gateshead 11, UK
5-1/2 in Diameter Pasltic
Front Scale: K, A (( B, C,) D, Log, Sin Tan)
Back: Instructions, Conversion Index, Abbreviations, S.I. Units, Notes
Scan provided by Michael Syphers of Illinos. His website is Following The Rules..


Davis Instruments T-S-D Computer

ISRM 14.07.02.96
Davis Instruments T-S-D Computer
Made in USA by Davis Instruments Corp., Hayward, CA.
6in Diameter Plastic
Front Scale (C&D scale): DISTANCE: Nautical or Statute Miles, KM or Yards (TIME: Minutes, Hours) SPEED
Back: Instructions
Gift Of Ed G. Millis, Dallas, Texas.
Ed Millis was at TI while the electronic 'slide rule' calculator was developed and is good friends with Jerry Merryman, the designer of the first calculator in 1967. Ed has also written a book on hobbies Hither, Thither and Yawn. Ed is a generous donor of over a hundred slide rules, calculators and ephemera to ISRM.


Miller Dial Circular Slide Rule

ISRM 13.02.23.01
Miller Dial Circular Slide Rule
Made in USA. Data Charts by Miller Dial,El Monte, Calif.
6in Diameter PaperBoard
Front Scale: D, ( C, CI, L, A, K)
Back: Instructions


General Industrial Slide Rule 1959

ISRM 14.01.10.10
General Industrial Slide Rule 1959
Made in USA. by Slide-chart Corp. PERRYGRAF Corp, Maywood, Ill.
for General Industrial Co., 1788 Montrose, Chicago 13, Ill. LOngbeach 1-5871
4in Diameter PaperBoard
Front Scale: D, ( C )
Back: Instructions
Gift of Bill Wehrend Collection, Palo Alto, California.


C-Thru S-96 Slide Rule 6in dia

ISRM 04.09.27.01.D1
C-Thru S-96 Slide Rule 6in dia
Made in USA - C-Thru Ruler Company, Hartford, Conn.
Front Scale: K, D, ( C, B, A, CI, L)
Back Scale: S, L, T
Back: Instructions


C-Thru PS-69 Proportional Scale 5in dia

ISRM 14.07.22.09
C-Thru PS-69 Proportional Scale 5in dia
Made in USA - C-Thru Ruler Company, Hartford, Conn.
Front Scale: Reproduction Size ( Size of Original, L) Percentage of Original Size, Number of Times of Reduction.
Back: Blank
Gift of Phillip Rodley, Upper Hutt, New Zealand.


REF SCA Circular Slide Rule
SCA Circular Slide Rule (1973)
Made in Australia by Slide Charts of Australia
Front Scale (Extended)
CI, C ( D, A, K, L)
Back Scale
Orginal Area (Conversion Factor, Converted Area)
Scan provided by Cyril Catt. Australia


Ground Water Hydrology Computer

ISRM 08.12.08.01

Ground Water Hydrology Computer - 4 coaxial disks 10mm thk
Made in USA by Info, Inc Newton, MA (1967) for Layne Associates, Memphis, TN
Front Scales - Transmissivity (T), Storativity (S), Time (t), Radius (r), factor (u), and Well Function of u [W(u)].
Back Scales - Well Function [W(u)], Transmissivity (T), Discharge (Q), Drawdown (s), and std. C, and D scales.
Solves This Non-Equilibrium Equation for Ground Water:
s = 114.6 Q W(u) / T; W(u) = e-u / u du; u = (1.87 r2 S) / (T t)
Donated by the designer, N. Thomas Sheahan, Research Geologist, Layne Research Division, Memphis, TN
Sheahan writes: "About 1,000 of the circular Ground Water Hydrology Calculator slide rules were produced... We had many of them printed with the names of the various associated Layne firms, but some were left blank to allow personalization. I continued to use this slide rule in the field and office from 1967 until the 1990s when I was finally able to get an HP-100LX, the first hand-held calculator that could solve this equation. Since then, I have had the slide rule as a wall decoration in my office until I retired this year (2008)".


Weems & Plath 105 Nautical Slide Rule

ISRM 04.04.22.05
Weems & Plath 105 Nautical Slide Rule
Made in USA by Weems & Plath, Annapolis, MD, 2002
Front Scale
Distance Naut Miles, Yards (Speed, Time Min, Hrs )
Back: Instructions on use
Owner: Mike Konshak's Personal instrument, used for USCG American Boating Course and Coastal Navigation traing.


Weems & Plath Tyler Slide Rule

REF
Weems & Plath Tyler Slide Rule 1966
Made in USA by Weems & Plath, Annapolis, MD,
Front Scale: Unique layout for solving Propertions, Multiplication and Division, Squares and Square Roots, and Functions of Angles
Back: Instructions on use
Archive - Rod Lovette Collection, UK.
Electronic Design magazine, V14-N13, May 2, 1966.Design Aids Column


Graphic Chemical Predictor

ISRM 11.05.24.01
Graphic Chemical Predictor
Made in USA by Dyna-slide Co. Chicago, Illinois - 8" diameter
Front Scales - Chemical Compunds, Oxidization Equations, Reduction Equations
Back Scale - Instructions
Donated by the children of Norman D. Fulton Jr.
Norman D. Fulton (1918-2010) used this Graphic Chemical Predictor during his career at Proctor and Gamble Co. He held various, positions at P&G heading up analytical labs, methods departments and other R&D areas where he could apply his knowledge and Sc.B. in chemistry. He retired in 1983 in Loveland, Ohio. His children, Ginger, Bobbie and Norman (Dudley) wanted to honor their father with this donation.


Helical Spring Design Computer

ISRM 13.00.00.71
Helical Spring Design Computer - 5 coaxial disks 10mm thk
Made (1977) by M.H. Mear & Co. Huddersfield, England for Associated Spring Corp (ASC)
Front Scale - Stress Calculator
Load, Spring Index, Ratio of Sides, Mean Dia (Dia of Wire, No.Coils (Deflection, Correction Factor))
Back Scale - Rate, Load and Deflection Calculator
Load, Spring Index, Ratio of Sides, Mean Dia (Dia of Wire, No.Coils (Stress, Modulas of Rigidity))
Donated by Jack Rababeh, Senior Engineer at ASC


Mascot Vest Pocket Slide Rule

ISRM 13.10.26.01

Instructions (1.51MB PDF)
Mascot Vest Pocket Slide Rule - 1934
Made or distributed in USA by Tavella Sales Compan, 25 West Broadway, New York, N.Y.
Note: Tavella Sales Co. also distributed the Gilson Midget at one time.
Material 0.7mm[0.067in) thick 69mm[2.72in] diameter plastic disk
Front Scale: L, D ( C, CI )
Back Scale: S, A, K, T


Mascot Vest Pocket Slide Rule

ISRM 13.10.26.01

Instructions (400KB PDF)
Mascot Vest Pocket Slide Rule - 1934
Made or distributed in USA by Tavella Sales Compan, 25 West Broadway, New York, N.Y.
Note: Tavella Sales Co. also distributed the Gilson Midget at one time.
Material 0.7mm[0.067in) thick 69mm[2.72in] diameter plastic disk
Front Scale: L, D ( C, CI )
Back Scale: S, A, K, T
Gift of Mr. Murphy of East Wanatchee, Washington


Cal-Co Patent Circular Slide Rule

ISRM 13.08.11.01


Photos of Francis Donchi, with European Ford Capri, and with grandson Nicolai Donchi, la Brianza, Italy.
Cal-Co Patent Circular Slide Rule
Made in Italy. Outer stator disk is 6.5 cm [2.6 inch], inner disk is 5.5 cm.
Country of origin based on 'SIN' being printed as 'SEN'
and metric HP conversion gauge mark of '736'.
Note: Appears to be painted/silkcreen on aluminum disks with brass hub. c1940
Front Scales: C ( D, A, K )
Back Scales: L, SEN 1, SEN 2, TG
Note: Concentric Sine scales
Donated by Nicolai Donchi, Monza, Italy in memory of his Grandfather Francis Donchi.
This artifact was found in the house of his Grandparents. and was owned by his Grandfather. Francis Donchi (1917-1993). Born in August 17, 1917 in Paina Brianza in Lombardy (Italy) where he finished elementary school and for the next 7 years, helped his father, Francesco, in the fields. At 18 he started working in a textile company on the banks of the River Lambro (Monza river) living modestly. At age 22 he was drafted into the Italian Army where he served with honor for 4 years from 1939 to 1943. After WWII he met his wife, who was a girl from his own village. Francis received a 'gratitude of war' after a few years for a lung disease due to breathing the toxic smoke created by the war industries. Though partially invalid he began a quiet life in Carate Brianza (Lombardy) and to have a child that carries on the family name. Francis had a second job restoring furniture in his house, which had many tools of the trade and where this slide rule was discovered after his death at age 76.


Latt-Mayer S.A. 42-8125 Circular Slide Rule

REF
Latt-Mayer S.A. 42-8125 Circular Slide Rule
Made by Latt-Mayer S.A., Rio De Janeiro. Approximately 5cm in diameter.
Front Scale
C (D)
Back: Promotion of Latt-Mayer product line (Portugese)
Archive - Photo by João Roberto Gabbardo collection, Brazil


US Army Signal Corps Psychrometric Calculator ML-322/UM

REF
US Army Signal Corps Psychrometric Calculator ML-322/UM
Made in USA by Virginia Plak Company 1944
Front Scale: DP, VP, C2, C1, t' ( t-t', P, THETA)
Back Scale: DP, VP, C2, C1, t' ( t-t', P, THETA)

Original Owner: John Vincent Atanasoff, (1903-1995) Father of the First Digital Computer, used while in the service during WWII. This scan of one of his three slide rules on display in the ISRM galleries that were provided by the Iowa State University Library, Atanasoff Archives. See also his model K&E N4080-3 S/N 798671 for an expanded biography


Cox Stadia Computer

REF
Cox Stadia Computer
Made in USA by Perrygraf - design by W. & L.E. Gurley
Front Scale: Difference of Elevation, Horizontal Difference
Archive - Not in Collection


Hemmi 1001 Circular Slide Rule

REF
Hemmi 1001 Circular Slide Rule
Made in Japan by Sun Hemmi
Front Scale
A, D( C, CI, B )
Back: TBD
Archive - Not in Collection


Norton & Gregory Roto-Rule 3.5" dia

REF
Norton & Gregory Roto-Rule - 3.5 inch dia
Made in England - Norton & Gregory, London -Pat Feb-12-1907
Front Scale : A, C, D, L
Archive - Not in Collection
Instruction Sheet 121Kb


Multor Currency Exchange

REF C26
C26 Multor Currency Exchange
Made in WestGermany - 3 color metal 8.8cm disk
Front Scale
D (C, A )
1.17Mb


Emeloid - Proportional Reproduction Size Finder

REF C22
Emeloid - Proportional Reproduction Size Finder
Made by Emeloid Operations, Hillside, NJ
6in (15cm) Dia Plastic Film disc
Front Scale
Reproduction Size ( Size of Original) % of Original Size, # times reduced )
Donated by Jack Rababeh, Senior Engineer at ASC


Graphic - Percentage Calculator

REF C23
Graphic - Percentage Calculator
Made by Graphic Calculator Co., Barrington, Illinois - 1962
6in (15cm) Dia Plastic Film disc
Front Scale
Sales ( % of Sales) or Number ( Percent )
Donated by Jack Rababeh, Senior Engineer at ASC


Graphic - Profit Finder

REF C25
Graphic - Profit Finder
Made by Graphic Calculator Co., Chicago, Illinois - 1954
8in (20.2cm) Dia Plastic Film disc
Front Scale
# of Items, Selling Price ( Markup, Profit )
Donated by Jack Rababeh, Senior Engineer at ASC


Ahrend Construction Disk

REF
Ahrend Construction Disk
Made in Netherlands by Ahrend
Archive - Herman van Herwijnen's SR Catalogue


Watham - Profit Finder

REF C24
Watham - Profit Finder
Made by Watham of Chicago - 1962
5-1/2in (14cm) Dia cardboard disc
Front Scale
# of Items, Selling Price ( Markup, Profit )
Donated by Jack Rababeh, Senior Engineer at ASC


Gong Se He Ying - Metalworking

ISRM 21.03.13.36
Gong Se He Ying - Metalworking calculator for Iron materials
Made in China by Sheyang DALI Metal Factory
Front Scale
degree, meter, quantity, kilogram (Steel. Iron, cast, ball, flat steel, flat iron, flat cast)
Back Scale
SG, A [ B, T Cot, ST, Sin Cos ] D, DI


Educational Instruments Corona 1

REF
Educational Instruments Corona 1 - c1965
Made in USA by Educational Instruments, Inc - 9cm Diam plastic
Front Scale: C, D, R (= DI), A, K, L, S, T, ST
Back:
The back, which has a window to the front disk for more surface area for equations, contains a mine of information. 112 formulae; 2 trig tables, 41 conversion factors 6 series expansions, 2 numerical integration formulae 13 numerical constants, 72 integrals, 36 differentials
Archive - Scan provided by Rod Lovette (UK) Collection


Lufkin Screw Thread Tap Drill Chart

ISRM 18.07.18.01
Lufkin Screw Thread Tap Drill Chart
Made in USA by Lufkin Rule Co. ©1935
Front Scale
National Coarse (size of Tap, Threads per Inch, Size of Tap Drill)
Back Scales: Screw Threads and tap drill sizes


Hutchinson Calculator No2 Gas Flow in Tubing

ISRM 18.03.20.14
Hutchinson Calculator No2 Gas Flow in Tubing 1956
Made in USA by Robert M. Hutchinson, Houston, Texas. Formulae by Mueller Co. Decatur, Illinos
Note: This is a 10" x 10" 6 page folder with instructions and a table.
Front Scale
D:Inches of Water, A:Cu.Ft.per Hour ( C:Length in feet, B:High Pressure, B':High Pressure, B:Low Pressure, B':Low Pressure, ) Cursor:Dividing Scale
Belonged to Robert N. Curry. Gifted by his friend Alice Bowling of Louisville, Kentucky.

Robert N. Curry was a 1949 graduate of Western Kentucky University. Bob was the head of Measurement for Texas Gas Transmission Corp and authored a book on Natural Gas processing Fundementals of Natural Gas Conditioning. He was former chairman of the AGA Transmission Measurement Committee. Several of his slide rules are currently in the ISRM galleries.



Edmunds Scientific Cal-Math Circular Slide Rule

REF
Edmunds Scientific Cal-Math Circular Slide Rule
Made in USA, Distributed by Edmunds Scientific.
Front Scale: D (C, K, A)
Archive - Photo from the internet



Ericsson Proportion Calculator Slide Rule

ISRM 13.00.00.87
Ericsson Proportion Calculator Slide Rule
Made in USA, 4.75 inch dia . Possibly used for finance.
Front Scale: 50 to 75 (10 +%, to, 10 -%)
Based on the equation on inner dial: to= (3600•1000•n)/(C x P)

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