Keuffel & Esser 4071 Duplex Slide Rule

This ten-inch mahogany duplex linear slide rule is coated with celluloid on the front and back only; the edges are bare. The indicator is glass with metal screws and plastic sides. On both sides, there is an A scale on the top of the base and a D scale on the bottom of the base. One side of the slide has B and C scales; there are BI and CI scales on the other side.

On the front (CD) side, the bottom of the base is marked: KEUFFEL & ESSER CO. N.Y.; PAT. JUNE 5. '00 DEC. 22. '08. The slide is marked on the left side: < 4071 >. The top edge of the indicator is marked: K&E.CO.N.Y. (/) PAT.8.17.15. The back of the rule is not marked.

Keuffel & Esser of New York sold this model of slide rule from 1901 to 1917. Head of manufacturing Willie Keuffel took out patents for improving the ability to adjust duplex slide rules in 1900 and 1908. The "frameless" style of indicator found on this example was introduced in 1915, after Keuffel's patent for that improvement was granted on August 15 of that year. Assuming that the indicator is original, the rule dates from 1915–1917. It sold for $5.00. Compare this example, donated to the Smithsonian by K&E in 1961, to the earlier versions MA.318477 and MA.326613.

References: Willie L. E. Keuffel, "Slide-Rule" (U.S. Patent 651,142 issued June 5, 1900); Willie L. E. Keuffel, "Slide-Rule" (U.S. Patent 907,373 issued December 22, 1908); Willie L. E. Keuffel, "Slide-Rule Runner" (U.S. Patent 1,150,771 issued August 17, 1915); Catalogue of Keuffel & Esser Co., 35th ed. (New York, 1915), 302–303.

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