Keuffel & Esser (K&E) 4012 Thacher Cylindrical Slide Rule, serial number 3596. Comprised of a brass core covered by paper marked with forty A scales, surrounded by an open rotating frame with twenty metal slats, each lined with cloth and covered with paper, marked with two B and two C scales. Wooden knobs on each end of the core rotate the instrument. The frame is attached to a mahogany base, all housed in the original wooden box with a hinged lid and brass hardware. Maker's marks to base and to two paper labels on interior of lid. Includes an instruction manual dated 1914. Core – 20" L x 4 1/2" dia. Overall with base – 5 1/2" H x 22 1/4" W x 5 3/4" D. Case – 6 3/8" H x 24" W x 6 3/4" D. Early/second quarter 20th century. Provenance: Private West Tennessee Collection. Note: Another example is in the collection of the Smithsonian Institute (see: https://americanhistory.si.edu/collections/search/object/nmah_690142). CONDITION: Some toning to cylinder. Some wear, scratches, natural wood shrinkage to case.