DescriptionPolyphase (Mannheim Type) 20" slide rule, 68 1608 (formerly 4053-5), made by Keuffel & Esser Co., New York, no date, circa 1962-1967. Mahogany, machined and laminated, with laminated white celluloid plastic ruled ("engine divided") scales in red and black; 21-5/8" overall length x 1-5/8" high x 3/8" thick. Indicator (cursor) is improved glass, no patent numbers or maker's markings. With: dark green leather case (sheath.) Date of this item is derived from information on the website of Clark W. McCoy with gratitude for his efforts. K&E logo on front slide at right end; model number at left end of slide.Slide inverts; serial number is at left end of slide, 950007. Back has the printed table of equivalents which is lacking the first inch at the left where a second K&E logo should appear. Scales are on the front: A, B, CI, C, D, K Slide inverts for scales: A, S, T, L, D, K (note that the scales S, T and L are marked on the right end of the slide.) Bottom edge is a centimeter scale divided to millmeters. Top edge is beveled with an inch scale divided in sixteenths. K&E had their main office and factories in Hoboken when this item was made.