A.W. Faber-Castell 360 Slide Rule
circa 1927–1934
A.W. Faber-Castell model 360 slide rule, manufactured in Bavaria, Germany, circa 1927–1934. Celluloid-faced pearwood construction, 28 cm (10 inch) scales, English-language conversion table on the back. Bears D.R. Patents 206428 (1907) and 365637 (1922). No case present.
This is an A.W. Faber-Castell model 360 slide rule, manufactured in Bavaria, Germany, most likely between 1927 and 1934. The model 360 was Faber's celluloid-faced standard Mannheim slide rule — the celluloid-laminated equivalent of the all-wood model 350 — introduced c.1895 and produced in multiple versions over four decades. Dating is established by three converging indicators: (1) the "Made in Bavaria" marking, used predominantly before c.1935; (2) D.R. Patent 365637, granted in 1922 and covering the adjustable slide-action screw mechanism, meaning the rule was made no earlier than 1922; and (3) auction and museum records of near-identical rules carrying the same two patent numbers with "Made in Bavaria" consistently dating to 1927–1934. The front of the slide bears the marking "A.W. FABER CASTELL / D.R. PATENT No 206428 No 365637." Patent 206428 (1907) covers the metal stability strips embedded in the stator and slide, described as one of Faber's principal design features and present on virtually every Faber wooden rule from c.1908 onwards. The front scales include a "Quot. +1" (quotient-plus-one) scale — a distinctive feature of early Faber designs. The rule measures 28 cm (10 inches) in scale length. The cursor is a metal-framed glass type embossed "MADE IN BAVARIA." The back of the stock carries a full English-language conversion table: Weight of Metals (per cubic inch), Chemical Equivalents (atomic weights), and Scale C/D conversion factors covering Imperial, US, and metric units — confirming the rule was made for the British or American export market. The rule is complete with its cursor but no carrying case. Acquired in February 2026 from Richard Gromett, Peddler Limited, Unit 6 Factory Units, Belton Lane, Grantham, Lincolnshire NG31 9HN (CRN: 08613665).
Significance
The slide rule was the primary calculating instrument of engineers, scientists, architects, and navigators for nearly three centuries. Before electronic calculators, every bridge, aircraft, pharmaceutical formula, and space mission was calculated on instruments like this one. Faber-Castell were the dominant European slide rule manufacturer, and their Bavarian-made rules represent the craft at its most refined — precision-engraved celluloid scales on pearwood, built to last generations. This rule dates from the interwar period, a time of extraordinary technological ambition in engineering and science, when every calculation was performed by hand and rule.