Keuffel & Esser  Mannheim 4098 A

This pocket 5 inches Mannheim model rule was produced between 1938-1946. Fabricated in the United States from white Xylonite (celluloid), this very simple model has only four scales on the front side: A-B and C-D, and on the back of the slider the scales S, L, and T. On the back side it has a 5 inches and a 13 cm ruler scales. This rule is a small copy of the K&E 4041. Its cursor was frame-less and made made of plastic. For more details see entries in National Museum of American History, and in McCoy's Catalogs. The original cost of this little rule ranged from 1.75 to $4.00 ($36 .00 to $82.00 in 2030 USD)

With these few scales, an skilled user was able to solve problems of the next math test, with a precision of two or three decimals:

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