Samuel Pepys, the ‘Father of the Modern Navy’, recorded in his Diary 14th April, 1663 ‘I walked to Greenwich, studying the slide rule for measuring of timber, which is very fine‘. It was a Coggeshall slide rule to help measure the dimensions, surface area, and volume of timber having the form of a folding carpenter’s measuring rule with a brass slide set into one arm and logarithmic scales.
Major historical developments in the evolution of the slide rule include:
1614 Invention of logarithms by John Napier, Baron of Merchiston, Scotland
1617 Development 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
1630 Invention of slide rule by the Reverend William Oughtred, London
1657 Development of the moving slide/fixed stock principle ay Seth Partridge, Surveyor and Mathematician
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
1900 Re-Introduction of log log scales by Professor Perry, Royal College of Science, London
1933 Differential trigonometrical and log log scales invented by Hubert Boardman, Radcliffe, Lancashire
The development of the slide rule arose after John Napier‘s publication of the concept of the logarithm and became most known in its linear form comprising three parts – a frame, a slide and cursor as illustrated above for the Faber Castell Slide Rule model 1/60. Lengths have properties that are analogous to those of numbers in some ways so that multiplication can be effected by the additions of lengths – hence the slide ruler can be considered to be the first analogue computer.
Construction
Faber Castell slide rules started out as boxwood, with celluloid facings added in 1897. Celluloid laminated mahogany was used from 1902 to 1912, followed by celluloid faced Pearwood. In 1952 all-plastic (Geroplast) versions were introduced. Slide rules made from pearwood date from the 1920’s to 1956. Around 1939 slide rules made in pearwood with metal inserts and a scale length of usually 25cm would have been given a number in the 1/xx series. The resilient base provides elasticity for the slide rule while the metal inserts provide stability and resist deformation caused by climate changes.
Date of Manufacture
Production of model 1/60 was from 1939 to 1943, then from 1952 to 1969 after the 2nd world war. More precise dating can be determined by the so-called blind date stamps and the engraving used for the company name. Thus from 1950 ‘CASTELL’ was printed on the left-hand or right-hand end of the scale.
Since 1920 coded blind date stamps appeared on the back of most slide rules giving the month and year of production. From 1930 to 1957 stamps on the left-hand side indicated the year and those on the right-hand side the month. On my slide rule the number ‘52’ is stamped on left hand side while on the right-hand side further stamps appear for the numbers ‘42’, ‘9’ and possibly the letters ‘lg’. Hence it would appear that the slide was produced in September 1952. It is not clear what the other stamps mean. A ‘MADE IN GERMANY’ stamp appears on the back.
A user guide for the slide rule is available here.
Company name and logo
From the beginning of the 1950’s the word CASTELL in italics was sandwiched between two castles. Also to be seen on my slide is the sign for Libra set of scales next to the company name A.W.Faber.
Company History The Faber-Castell company was founded in 1761 by Kasper Faber, a member of the noble family ‘The House of Faber-Castell’ in Bavaria. Kasper was a cabinet maker who started to manufacture pencils in Stein near Nuremburg. Kaspar Faber’s great-grandson, Johann Lothar Freiherr von Faber, expanded the company by opening branches in New York, London, Paris, Vienna, and St. Petersburg.
The company also began offering art products other than pencils, opening a slate factory in Geroldsgrün, Bavaria, where slide rule production began in 1892.
From the late 1800s to late 1970s Faber-Castell became one of the world’s major manufacturers of slide rules.
Some past users of slide rules
Sources of Information
A detailed and comprehensive analysis of Faber Castell slide rules by Peter Holland (V8.1) can be downloaded here. It is from the German slide rule site where any updates to this document can be obtained.
Other sources include:
Details of Faber Castell slide rules on Spanish site
Slide rule museum