We are sure that this was in the early 1960s while they were working through old 4000 series stock.
Post sold a wide variety of slide rules, both under its own name and under the names of various manufacturers.
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).
1944 - The word 'POST' surrounded by an ellipse becomes the permanent logo.
Fred Post goes to work at Eugene Dietzgen's company. Removal of the "N" prefix also indicated a variation in the model.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.Dating a slide rule becomes difficult if a manufacturer did not imprinting a date code or serial number on the stock. This comprehensive research will enable you to find the period of manufacture for most every Dietzgen slide rule from 1887 through 1972.Even then, some manufacturers recycled their serial numbers over time, and the stock could have been left on a shelf for a period of time before the slide rule was assembled and shipped. Combined Large 6.47MB Most Keufel & Esser slide rules had serial numbers, but unfortunately they reused their 6-digit serial numbers several times.The Bruning boys work for another blueprint company. 1893 Frederick Post, Charles Bruning, and Jacobi form their own blueprint company in Chicago under the name Post, Jacobi, & Bruning. 1962-1975 -The numbers were converted to a 68-xxxx number series. The downloadable charts are a matrix of Dietzgen slide rules, catalogs and price lists that was compliled by Bruce Babcock, Ph. and was published in the Journal of the Oughtred Society (JOS) October 1996, Volume 5, Number 2.Dates that a design was registered or patented only suggests an approximate year a model may have been first produced, as the model may have been distributed a year or more before issuance (patent pending). There were three rollovers occurring in 1943-1944, 1954, and 1962.The patent may only refer to a certain combination of scales used over a thirty year time on different models. 1911 James Dieterich, who has worked his way up to blueprint foreman at B. Makepeace Co., goes west and lands a job as a salesman with the K&E branch in San Francisco. In general the production rate was about 70,000 rules per year until the 1950s. The 1960s had a production rate of about 100,000 per year for several years and tapering off in the 1970s ending at about 700000.1963 - The change from state abbreviations to two letter codes (Colo. to IL) 1967 - The use of 5 digit Postal Zip Codes in USA addresses now mandantory. 1896 Charles Bruning leaves Post & Jacobi, and after a honeymoon in Europe, returns to the US and settles in NYC. He sells his blueprint business interests to George W. 1899 In April, Charles Bruning returns to NY and starts the Charles Bruning Co. The Fuller and Thacher's slide rules had their own serial number systems. There were logical groupings of numbers and dash numbers were used to depict length variations of a given rule type.1983 - The use of Zip 4 Postal Zip Codes began used by USPS Many of the founders of United States firms producing slide rules had their roots as employees in other firms, just as modern entrepenuers break off from their employers and create their own start-up companies. Gustavson, in her article Necessity is the Mother of All Invention (Modern Reprographics, June 2000) is a good example. "N" was used as a prefix many times to denote some change in a given model.