DescriptionMerchants' slide rule (Mannheim type), 10", model 4094, made by Keuffel & Esser Co., N.Y. No date, circa 1936-1937. Mahogany, machined and laminated, with laminated white celluloid plastic ruled ("engine divided") scales in red and black; bottom edge has laminated scale with centimeters; top front edge beveled with laminated white celluloid ruler, English measure by inches and sixteenths; 10-5/8" overall length x 1-5/16" high x 3/8" thick. Indicator (cursor), "K&E Co. N.Y. Pat. 8, 17, 15." Back has an inset printed table of settings, formulas and ratios. Serial number: 507540. No lot number. Lacking original case. With: two different printed instruction manuals, catalogued separately as archives 2009.006.0150.01 (which is for this rule) and .0150.02 (which is for Merchant's rule 4095.) The first manual includes the Detroit office opened in 1936 which helps to date the issue of this rule. Scales, at left: DF CF CI C D Back of slide is blank except for serial number. Dated from the serial number. Marked on face: Keuffel & Esser Co. N.Y.; Pat. 1,934,232; Made in U.S.A. Model number is marked on right end of rule. K & E main offices and factories were in Hoboken during this period.