1944 - The word 'POST' surrounded by an ellipse becomes the permanent logo.
1946-1950 - Post resumes rebranding Hemmi slide rules, rules marked "Made in Occupied Japan".
Catalogs are an excellent indication of when a model was produced or discontinued. This chart was developed by Ed Chamberlain to help determine the date of manufacture, but one must first zero in on which period the slide rule was made.
Sometimes the copyright date in a manual is used to determine the approximate age, but one printing could span several decades. Look at catalog's in the museum library and visit Clark Mc Coy's: Serial numbers started in 1924 beginning with 0 and going through 999999 then rolling over to 0 again.
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.
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.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.1903 to c1917 Slide rules manufactured by Dennert and Pape c1920 to 1924 Slide rules manufactured by Nestler; Koch, Huxhold & Hannemann; and possibly Faber-Castell.1924 to 1930 Slide rules manufactured by Koch, Huxhold & Hannemann.