Keuffel & Esser 4080  Log-Log Duplex Trig

The 4080 Log-Log Duplex models were manufactured in the United States from 1937 until 1954. Fabricated with mahogany wood, was fully covered with white celluloid were scales were engraved, and it was hold with metallic braces. The indicator was made with glasses hold on plastic ends with screwed metallic frames. This rule, -primarily designed to solve science and engineering problems-, has 20 scales, 10 per side, standing out the log-log scales to solve natural exponential and logarithmic equations, a scale for base 10-log, and an additional scale for the sine and tangent values for small angles (from 34' to 5 degrees  40'). 

The 4080 family replaced the 4091 and 4092 models. During these 17 years, K & E produced different versions of this model; in some versions the scales only changed their positions on the rule, but in other versions some scales were changed (See the 4080 model section on K&E Standard page of the ISRM Website). An important characteristic of this model was that the trigonometric scales are Sexagesimal (Base 60), these were divided in degrees and minutes. 

The 1942's 4080-3 and 1940's 4081-5 models of my collection have on the front face the next scales: LL0, LL00, A [ B, T, ST, S ] D, DI, K, and on the back face: L, LL1, DF, [ CF, CIF, CI, C ] D, LL3, LL2, where the scale in parenthesis are on the slider.  The original price of the 4080-3 was $ 13.50 ($ 256.00 USD in 2023), and the original price of the 4081-5 was $ 29.00 ($594.00 USD in 2023).

In the early 1940's the 4080 models evolved to the 4081 Log-Log Duplex Decitrig where the angles in the trigonometric scales were also degrees but in decimal format, and the Log-Log scale on LL0 and LL00 was extended to three scales: LL01,LL02, and LL03. 

In the second half of the 1950's, a new evolution occurred. In the the new 4181 model the ST (Sine-Tangent) scale was changed to the SRT, where R stands for Radian. Whit this new scale was possible to convert angles in degrees into radians and viceversa.

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