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1951 - Hemmi creates the Post Versatrig (1450) and Versalog (1460) Slide rule exclusivly for the North American Market.1957 - Success of the Versalog prompts Hemmi to make pocket versions, the Post pocket Versatrig (1451) and Versalog (1461).The dash number scheme for length variations was abandoned.
COPYRIGHT XXXX and © XXXX 1943 - 2 digit Postal Zone codes to increase efficiency of delivery because of a wartime shortage of staff. 1963 - The use of 5 digit Postal Zip Codes in USA addresses adopted but not mandantory. 1898 After a fire, Bruning rebuilds the New York Blueprint Paper Co., only to close it and return to Chicago. It is not uncommon to find rules in the 1960s in 68 xxxx series packaging but 4000 series model numbers on the rules.
Post also sold branded slide rules from Richardson, Vicari, Boucher, Sexton, Halden, Chandler, Ritow and Winslow.
See Who Actually Manufactured Frederick Post Brand Slide Rules, By Paul Ross c1890 - Frederick Post founded in Chicago to manufacture and sell drafting, engineering and surveying supplies.
1931 to 1941 Slide rules manufactured by Hemmi Seisakusho.
1932-1941 - Hemmi-manufactured rules have no date code and are marked "Made in Japan" 1942-1946 - WWII.