Dating faber castell slide rules
December, 1967 - Teledyne Acquires Frederick Post, slide rules sold under both the Post and Teledyne Post names. Still labeled as Post 1970 - Versalog II Date codes from 1970 are now labeled as Teledyne Post 1972 - The Frederick Post brand name disappeared and the Teledyne Post '44' numbering system was introduced. The date code (see Hemmi) is in the form 'HF' where the first letter identifies the year according to the system 1951 = B, 1952 = C, 1953 = D, etc., and the second letter identifies the month according to the scheme A = January, B = February, C = March, etc. The first letter is the year, as is listed in the following table.
Thus, 'HF' indicates a slide rule made in June 1957. The second letter, restricted to either S or K is assumed to be the manufacturing location.
Post itself actually made no slide rules; even those rules that bore the Post brand name were manufactured by others.
See Who Actually Manufactured Frederick Post Brand Slide Rules, By Paul Ross c1890 - Frederick Post founded in Chicago to manufacture and sell drafting, engineering and surveying supplies.
1950 - Two character date codes appear (see Hemmi date codes).
1951 - Hemmi drops the "Occupied" and marks slide rules "Made in Japan" or just "Japan".
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.