The top edge of the rule is marked: PATS. PEND. MADE IN U.S.A. 4083-5 LOG LOG DUPLEX VECTOR ® COPYRIGHT 1947 BY KEUFFEL & ESSER CO. PATS. 2,500,460 2,168,056 2,170,144 2,285,722 2,422,649. See 2007.0181.01 for a description of these patents. There is a green leather case with metal inlays on the holder for the flap. One of the inlays is marked: PAT. 2,000,337. The flap is marked: K + E. Adolf W. Keuffel applied to patent his method for securing a slide rule case on November 1, 1932, and received the patent on May 7, 1935.
Keuffel & Esser of New York used this set of scales on this model number from 1955 to 1962. The serial number is consistent with a date later in this time frame. The rule sold with the leather case for $56.50 in the 1950s.
References: Adolf W. Keuffel, "Slide Rule Case" (U.S. Patent 2,000,337 issued May 7, 1935); K + E Catalog, 42nd ed. (New York: Keuffel & Esser Co., 1954), 280–281; Keuffel & Esser Co., "Price List Applying to the 42nd Edition Catalog" (New York, June 1, 1956), 43; Clark McCoy, "Collection of Pages from K&E Catalogs for the 4083-3 Family of Slide Rules," http://www.mccoys-kecatalogs.com/KEModels/ke4083-3family.htm; Ed Chamberlain, "Estimating K&E Slide Rule Dates," 27 December 2000, http://www.sphere.bc.ca/test/ke/320-k+e_date2.jpg.