Keuffel & Esser 4090 Universal Duplex Slide Rule

This ten-inch wood slide rule is faced with white celluloid on both sides. The indentations on the metal end pieces face in, as was typical for Keuffel & Esser slide rules manufactured between 1901 and 1913; compare to MA.326613. The brass indicator is in the double chisel style (with an open interior), used from 1891 to about 1909. See also MA.318477 and 1977.0370.01. The edge of the indicator is marked: KEUFFEL & ESSER CO. (/) NEW-YORK.

The slide has two parts, which fit between the three parts of the base. On one side, the top of the base has an A scale; the top of the slide has B and C scales; the middle of the base has D and DF scales; the bottom of the slide has C and S scales; and the bottom of the base has an A scale. The bottom of the base is marked: KEUFFEL & ESSER Co NEW-YORK. On the left edge of the rule, the top and bottom of the base and the slide are all stamped: 5.

On the other side, the top of the base has an A scale; the top of the slide has BI and CI scales; the middle of the base has D and DF scales; the bottom of the slide has CIF, L, and T scales; and the bottom of the base has a D scale. On both sides, the DF scale is unlettered. The CIF scale is incorrectly lettered "CI." Unlike later slide rules, which start at pi, the folded scales on this rule (CF, CIF, and DF) start at the square root of 10 (approximately 3.16).

The bottom of the base on the back is marked in red: PAT. OCT. 6. 1891 & MAR. 21. 1899. The second patent date is in a different font and size than the first. The first patent refers to William Cox's invention of the duplex slide rule, which K&E used to launch its manufacture of American slide rules. William L. E. Keuffel, the company's head of manufacturing, received the second patent for the design of the dual slide seen in this rule.

K&E only used the dual slide on its Universal slide rule, suggesting the concept was not as useful as the company hoped. The dual slide also addressed a limitation of K&E dividing engines, which were only able to cut scales on the edges of rules. Once K&E improved its dividing engines, this solution was no longer necessary. The Universal slide rule sold as model 4090 from 1900 to 1905 and as the model 4090N from 1906 to 1911. From 1900 to 1902, it had a brass chisel indicator; from 1903 to 1905, it had a German silver chisel indicator; and from 1906 to 1911 it had a glass clam shell indicator. This example thus dates to 1900–1902. It sold for $20.00.

References: William Cox, "Engineer's Slide-Rule" (U.S. Patent 460,930 issued October 6, 1891); W. L. E. Keuffel, "Slide Rule" (U.S. Patent 621,348 issued March 21, 1899); Catalogue of Keuffel & Esser Co., 30th ed. (New York, 1900–1901), 297; Catalogue of Keuffel & Esser Co., 31st ed. (New York, 1903), 307; Bob Otnes and Bob DeCesaris, "The K&E Universal Slide Rule," Journal of the Oughtred Society 10, no. 2 (2001): 45–48; Bob Otnes, "The 31st (1903) and 32nd (1906) Editions of the K&E Catalogue," Journal of the Oughtred Society 11, no. 2 (2002): 24–32.

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