Keuffel & Esser 4081-3 Log Log Decitrig Duplex Slide Rule

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This 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 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,"; Ed Chamberlain, "Estimating K&E Slide Rule Dates," 27 December 2000,; K + E Price List, Applying to the 42nd Edition Catalog (Hoboken, N.J., 1959), 73.
Currently not on view
date made
Keuffel & Esser Co.
place made
United States: New York, New York
Physical Description
mahogany (overall material)
celluloid (laminate material)
glass (cursor material)
metal (part material)
overall: 1 cm x 32 cm x 5.2 cm; 13/32 in x 12 19/32 in x 2 1/16 in
ID Number
catalog number
accession number
Credit Line
Gift of Keuffel & Esser Company
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
Data Source
National Museum of American History


In the academic year 1956-7 I acquired a model 4081-3 from a K&E sales rep. The serial number is 905366. Not sure if this is helpful for dating because K&E recycled their 6-digit serial numbers. The matching K&E leather carrying case is Model 4092-3S. K&E also sold leather belt clips that enabled students to wear their slide rules like swords. An annual visitor to the campus brought an engraving machine to personalize slide rules with the owners' names.. After a busy day or two, he moved on to the next college. Post was K&E's main competitor. Post slide rules had bamboo cores that provided very smooth movement, important for precise settings. Hope this is of interest.

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