DescriptionLog Log Duplex Trig 20" slide rule, 4080-5, made by Keuffel & Esser Co., New York, no date, circa 1940-1942. Mahogany, machined and laminated, with laminated white celluloid plastic ruled("engine divided") scales in red and black; 22-3/8" overall length x 1-9/16" high x 3/8" thick. Lacking indicator (cursor.) Accompanied by reddish brown leather case (sheath); flap closure missing. Model number for this twenty inch Mannheim type rule appears at on front slide at right end, the "5" indicating its length. Serial number, 923622, appears on back slide at left end and again, when looking at the back, on the bottom left edge of the stator. Even without the indicator, the serial number and patents suggest the early 1940s as the manufacture date. Scales are on the front: LL1, DF, CF CIF, CI, C, D, LL3, LL2 Scales are on the back: LL0, LL00, A, B, T, ST, S, D, DI, K Manufacturer's mark and patents on front at top center: Keuffel & Esser Co., N.Y.; Pats. Re. 20,894; 1,930,852; 2,170,144; Pat. Pend.; Made in U.S.A. K&E had their main office and factories in Hoboken when this item was made.