1957 KEUFFEL & ESSER 4081-3 LOG DCITRIG DUPLEX SLIDE RULE

Ten-inch mahogany duplex slide rule is coated with white celluloid. There are LL02, LL03, DF, D, LL3, and LL2 scales on one side of the base, with CF, CIF, CI, and C scales on the slide. The right side of the slide is marked in red: © (/) K + E. On the other side of the base, there are LL01, L, K, A, D, DI, and LL1 scales, with B, T, SRT, and S scales on the slide. The left end of the slide is marked: 320858. The left end of the top and the bottom of the base are both marked: 858. The indicator is glass, with white plastic edges held together with metal screws. Keuffel & Esser used this arrangement of scales on this model from 1955 to 1962; the serial number suggests this example was made around 1957. 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 dec