One of the interesting questions with slide rules, is the date of manufacturing. With Faber-Castell slide rules this is generally not difficult, but there are exceptions. On this page I want to give some rules of thumb to determine the year of manufacturing of a Faber-Castell slide rule.
Date stamp on the back
Most Faber-Castell slide rules have on the back 2 embossed stamps that give the year and month of manufacturing. Mostly the left number gives the year, the right number the month.
For the year stamp, in most cases the following rules apply:
- 2-digit numbers: the year of the 20th century. E.g. 34 means 1934.
- 1-digit numbers: the year of the second decade of the 20th century. E.g. 3 means 1923. 1-digit numbers were only used between 1920 and 1929.
- Before 1920, slide rules had no date stamp, but, there are also plenty of rules after 1920 that do not have a date stamp.
Type numbers
All slide rules with a 3-digit type number starting with a 3 (like 342 or 360) were manufactured before 1935.
All slide rules with a mixed type number (like e.g. 1/60/360) were manufactured around 1935-1938, when Faber-Castell changed from the old 3-digit number scheme to a newer 2-number numbering scheme. E.g. model 360 (pre-1935) changed to model 1/60/360 (in 1935-1938), changed to model 1/60 (after 1938). Often the typeface of the old number (360) is slightly different form the 1/60.
Before 1910, slide rules did not have a type number.
Plastic slide rules which start with 111 (like e.g. 111/87) or 57 (like 57/89) were manufactured as of 1952.
Materials being used
Slide rules entrely made of plastic only appeared in 1951. Before that, all slide rules were wood with a plastic/celluloid layer laminated on top, or pure celluloid.
Manufacturing techniques
All wooden slide rules manufactured after 1909 have a split stator which gives some flexibility to the strength with which the slide is held. Older slide rules have a stator in one piece.
Most wooden slide rules manufactured after 1908 have small, tapered, hardwood pins to fasten the celluloid scales to the wood of the stator or the slide. Earlier slide rules do not have these pins. However: many low cost models manufactured after 1908 lack these pins.
The longer 20-inch slide rules sometimes have adjustment screws in the long side that can be used to adjust the gap between the 2 stator halves. This feature only occurs after 1922.
Logos being used
The oldest Faber-Castell slide rules mention that they were made in Bavaria (instead of Germany). Most "Made in Bavaria" slide rules that I have seen, date from before 1920, but I have seen occasional ones as young as from 1928.
The oldest Faber-Castell slide rules have the name A.W. Faber. in gold on their front face. The oldest one with this logo that I know, dates from 1909.
The "* A.W. Faber." logo can be found on sliderules made till about 1920.
Around 1920 the name "Castell with 2 lying castles appears in the logo. This logo is being used till about 1928.
As of 1928, the * in the logo is replaced by a pair of scales. This logo is being used till about 1942. Often the logo is accompanied by other text.
In the years up to about 1938, there is often one or more indications of patent numbers or the term DRP or DRGM.
In the years 1938-1942 the model number is often preceded by "Castell"and followed by the model name. Like e.g.:
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