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

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

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Usage conditions apply
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
Object Name
slide rule
date made
Keuffel & Esser Co.
place made
United States: New York, New York City
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
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I have my father's slide rule, dating from the late 30's (K&E introduced it in 1937). He worked at the Electro Motive Company on the early diesel electric locomotives. He ended his career at Martin Marietta Aerospace, working on the Titan IIIC and Apollo programs. I entered college in 1975, and much to dad's horror I opted for an HP-25C instead of a slide rule. Oh the joy I felt when I figured out how to convert polar to rectangular on it!
In 1959, my buddy, Al, and I, went downtown, Philly, to the K+E store to get my "slip-stick", so I could be ready to start my first semester in Engr at PSU. I paid the princely sum of $22.50, no tax, for it. My wife thinks I still have it, but I can't find it. I recall that Pickett was another brand, yellow, I think, but not nearly as good as the K+E. I also recall that the first Engr class, Engr-1, was how to use the slide-rule, and featured a 10 foot model that the instructor, good 'ol Charlie Sohl, used in class. The text book was the K+E manual, with the examples given as home work and tests. Yes, I did graduate with a BS in ARoE, then went on for an MS. Retired from AREVA in 2014 after building lord knows how many nuclear plants, at the ripe old age of 73. BTW, also had a circular one, a double sized one, and a 6 inch one, just to complete the set.
I recently acquired a 4081-3, serial no 898379, with leather case, at a flea market for $2.00. I was a BEE major at San Diego State University class 1982-87. One prof required us to learn the slide rule before we could use a calculator. He had a box full of K&E 4081-3 slide rules for our use. I enjoyed it so much that I purchased one. Unfortunately, it was lost somewhere along my travels. Having fun learning again how to use this amazing piece of technology.
My father got this, Model 4081-3, in the late 40's or early 50's. Took it to college with me in 1967 and obviously was a important tool. Has another patent no., 1,930,853 and a RE 20,984 on it. There's a 116642 on the back of the slide.
I bought mine used on entering GA Tech in 1950. It has same pat. nos. as the one described above. I used it during my time at Tech from 1950 to 1959 when I graduated BEE. Had to give a little time to the USMC during that time, remember "Trumans' police action". I doubt that I could solve the simplest problem in EE on the slide rule now. I had it framed in a box frame many years ago. Still looks good.
When I enrolled in Civil Engineering at Mississippi State University in 1965, the school published, in their catalog, a requirement for all student to take a course in slide rule and recommended the K& E slide rule as fulfilling the requirement for CE-the Log Log Duplex was for other majors due to the decimal trig functions. I still have the leather case that came with mine but not the belt clip that allowed us to wear it like a sword. The slide rule marked us as the “elite” of the student body. I moved on to the HP 35 calculator within a few years.
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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