The top edge of the rule is marked: PATS. PEND. MADE IN U.S.A. 4081-3 LOG LOG DUPLEX DECITRIG ® COPYRIGHT 1947 BY KEUFFEL & ESSER CO. PATS. 2,500,460 2,168,056 2,170,144 2,285,722 2,422,649. These patents were issued between 1939 and 1950. They dealt with the arrangement of scales on a slide rule, in particular so that the user could solve multistep problems without having to write down intermediate settings, and with the placement of a legend to make placing the decimal point easier.
The Keuffel & Esser Company of New York donated this slide rule to the Smithsonian in 1961. In 1959, model 4081-3 sold for $22.50. Model 4081-3, the Log Log Duplex Decitrig, differs from model 4080-3, the Log Log Duplex Trig, in that the degrees on the trigonometric scales are divided into decimals instead of into minutes. Compare to 1992.0437.01 and 2007.0181.01.
References: Carl M. Bernegau, "Slide Rule" (U.S. Patent 2,168,056 issued August 1, 1939); Lyman M. Kells, Willis F. Kern, and James R. Bland, "Slide Rule" (U.S. Patent 2,170,144 issued August 22, 1939); Lyman M. Kells, Willis F. Kern, and James R. Bland, "Slide Rule" (U.S. Patent 2,285,722 issued June 9, 1942); James R. Bland, "Slide Rule" (U.S. Patent 2,422,649 issued June 17, 1947); Herschel Hunt, "Slide Rule" (U.S. Patent 2,500,460 issued March 14, 1950); Clark McCoy, "Collection of Pages from K&E Catalogs for the 4081-3 Family of Slide Rules: 4080-3 & 4081-3 Family Groups," http://www.mccoys-kecatalogs.com/KEModels/ke4081-3family.htm; Ed Chamberlain, "Estimating K&E Slide Rule Dates," 27 December 2000, http://www.sphere.bc.ca/test/ke/320-k+e_date2.jpg; <i>K + E Price List, Applying to the 42nd Edition Catalog</i> (Hoboken, N.J., 1959), 73.
