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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.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.All Post slide rules with "Made in USA" come from this period.
1951 - Hemmi creates the Post Versatrig (1450) and Versalog (1460) Slide rule exclusivly for the North American Market.
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.
Found on manuals and other slide rule ephemera: 1909 - Copyright Act on published works passed by Congress. 1951 - 3 digit Area Codes in Phone numbers implemented by AT&T (Developed in 1947). 1897 New York Blueprint Paper is founded by Charles Bruning in January. The common rules were produced in regular batches but the specialty rules did not sell as well and a given batch of rules might stretch over several years.
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.
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.