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.
Later in the year, the two buy out Bruning's interest and form Dieterich-Post Company.
Huey acquire the coating rights to Bruning products and start the Huey Company. opens a branch in San Francisco and puts Frederick's nephews, Rudolph and Victor Post in charge. 1921 Rudolph Post recruits Jim Dieterich from K&E and obtains financing for a blueprint operation from his uncle, Charles Bruning.
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.
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.
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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.
Post itself actually made no slide rules; even those rules that bore the Post brand name were manufactured by others.
At one time or another Post brand slide rules were made by Dennert & Pape, Nestler, Faber, Hemmi, Lawrence Engineering Service, Charvoz-Roos, Bruning and Gilson.