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The dash number scheme for length variations was abandoned.
There are numerous examples of 68 xxxx series numbers on retail boxes and the slide rule inside has the old 4000 series number on it.
1946-1950 - Post resumes rebranding Hemmi slide rules, rules marked "Made in Occupied Japan".
1950 - Two character date codes appear (see Hemmi date codes).
1970 - Post becomes Teledyne Post in 1970, slide rules sold under both the Post and Teledyne Post names.All these firms produced slide rules under their name as well as their primary business of drafting supplies: 1867 Keuffel & Esser, form an engineering supply house 1878 Eugene Dietzgen immigrates from Germany and settles in New York where he goes to work for Keuffel & Esser, now 11 years in business in the US. 1880 The Bruning family arrives from Nyborg, Denmark and settles in Cincinnati. 1885 Eugene Dietzgen starts a business in Chicago that later becomes the Eugene Dietzgen Co. Charles Bruning, his brother Jacob, and cousin Frederick Post arrive in Chicago. The use of the "N" prefix is not always consistent.Fred Post goes to work at Eugene Dietzgen's company. Removal of the "N" prefix also indicated a variation in the model.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.