Keuffel & Esser 4081   Log-Log Duplex Decitrig

The 4081 Log-Log Duplex Decitrig family was manufactured in the United States from 1937 to 1972. A twin model of the 4080, this also very popular rule was fabricated on a mahogany frame with celluloid laminated to the surface where scales were engraved, with glass cursor screwed to plastic ends with metallic frames, and hold with brass braces.  It was produced in two sizes: 4081-3 (12 inches) and 4081-5 (22 inches). In 1962 the model numbers renamed to 68-1210 and 68-1200 respectively, and a Ivorite version of the 4081-3 was introduced, the Jet-Log, with an additional scale: DI.

The 4080's and 4081's basically had the same scales, but the trig scales on the 4080's were divided in degrees and minutes while on the 4081's were divided in degrees and decimal degrees. During the 35 years the 4081's were produced, the number of scales varied from 20-21, changing the number of Log-Log scales and adding/ removing the DI scale. 

The pocket version of the 4081 model, the 5 inches 4181-1, was first advertised in the 1952 catalog. With the same set of scales as the 10 inches model: Front Scales: LL01, L, K, A [ B, T Cot, ST, S Cos ] D, DI, LL1, and Back Scales: LL02, LL03, DF [ CF, CIF, CI, C ] D, LL3, LL2, the 4181-1 was a compact but powerful engineering tool. The original cost of this pocket rule shown in the 1953 price catalog is $9.25 ($104.22 in 2023 USD), while the 4081-3 is priced $22.50 (253.52 in 2023 USD)

Click on the next links to see professional panoramic pictures of the 4081 model. 

4081-3 (1937)

4081-3 (1947)

4081-3 (1950)

4081-3 (1952)

4081-3 (1954)

4081 (1955-1962)

References:

• McCoy, Clark: Keuffel and Esser Catalog Site. K&E Catalogs and Price Lists for Slide Rules.  http://www.mccoys-kecatalogs.com/KEmain.htm 

This website is the most extensive digitla file of Keuffel and Esser product catalogs and price lists (prices  shown here were taken from these lists)  from 1881 until 1972. You can find also user manuals for many slide rule models, as well as other interesting brochures and materials.

• Shawlee, Walter: Keuffel & Esser Co. Slide Rules. https://www.sphere.bc.ca/test/ke-sliderule.html 

This website gives a good overview of models, and other interesting information and links