Keuffel & Esser 4090-3 Log Log Trig Duplex Slide Rule

This ten-inch mahogany duplex slide rule is coated all around with white celluloid and held together with L-shaped metal end pieces. The front of the base has LL0, A, T, S2, and S1 scales, with B, K, and CI scales on the slide. The LL0 scale is a log log scale of decimal quantities. The A and B scales are identical, divided logarithmically from 1 to 10 twice in the length of the scale in the usual manner. The K scale is also divided logarithmically, but three times in the length of the scale, for use in finding cubes and cube roots. The CI scale is divided logarithmically from 1 to 10 the length of the scale, going in the opposite direction from the A and K scales. The T scale is a scale of tangents and cotangents, doubly numbered with angles given in degrees and minutes. The S1 and S2 scales are scales of sines and cosines, doubly numbered. The top of the base is marked in red: KEUFFEL & ESSER CO.N.Y.; PAT. APRIL 1.'24 OTHER PAT. PENDING; MADE IN U.S.A. The left end of the slide and the front of the rule are marked with a serial number: 448333.

The back of the base has L, LL1, DF, D, LL3, and LL2 scales, with CF, CIF, and C scales on the slide. The right end of the slide is marked in red: < 4090-3 >. A glass indicator has white plastic edges held together with metal screws. One edge is marked: KEUFFEL & ESSER CO.N.Y. The other is marked: PATENTED AUG.17.15. (/) OTHER PAT. PENDING.

Keuffel & Esser advertised model 4090-3 from 1933 to 1936. However, the combination of scales on this example was only issued in 1933, when the rule sold for $10.00. The serial number is consistent with this date. In 1937, model 4090-3 was replaced by model 4080-3.

References: Adolf W. Keuffel, "Log Log Duplex Slide Rule" (U.S. Patent 1,488,686 issued April 1, 1924); K&E Slide Rules and Calculating Instruments (New York, 1933), 10–11; Catalogue of Keuffel & Esser Co., 38th ed. (New York, 1936), 316–317; Dieter von Jezierski, Slide Rules: A Journey Through Three Centuries, trans. Rodger Shepherd (Mendham, N.J.: Astragal Press, 2000), 71–75; Clark McCoy, ed., "Collection of Pages from K&E Catalogs for the 4090-3 & 4091-3 Family of Slide Rules," http://www.mccoys-kecatalogs.com/KEModels/ke4091-3family.htm.

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