1950s dating guide
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.1946-1950 - Post resumes rebranding Hemmi slide rules, rules marked "Made in Occupied Japan".
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.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.Having contact with the original owner of a slide rule that remembers the year it was purchased helps on determining the age. In general it is safe to assume a linear production rate between the rollover dates particularly for the common types rules.Other Slide Rule dates are currently in development. Please refer to the museum library and individual galleries as this page is being built. Serial numbers can be used to approximate the manufacture date of a given rule however not necessarily the sales date.
1951 - Hemmi drops the "Occupied" and marks slide rules "Made in Japan" or just "Japan".