Guide - Hemmi Date Codes Greg's Slide Rules
Hemmi/Post/Hughes-Owens Date Codes



After Hemmi dropped the 'Made in Occupied Japan" logo in about 1951 they began placing date codes on certain rules. This code took the form of a two letter code marked somewhere on either the top or bottom of the rule. This code gives the year and month of manufacture and allows the rule to be dated fairly accurately.

Depending upon the age of the rule the code may be in a different location. Older Post Versalog rules will have the date code on the top of the rule following the "Hemmi Bamboo - Japan" and they will be coloured. Here is a sample:

Late in 1958 Hemmi moved the date code from the top of the rule to the bottom near one end of the rule and stopped colouring it. To find the date code you need a good strong light and sometimes a magnifying glass as the imprint is very small and quite faint. I was unable to get an example to show up using a scanner as the markings do not stand out at all.


Code Details



There are two code segments, The first letter indicates the year of manufacture, the second letter then indicates the month of manufacture.

Year Code:

A B C D E F G H I J K L M
1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962

N O P Q R S T U V W X Y Z
1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975

Month Code:

A B C D E F G H I J K L
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec


Samples Explained



With the above codes explained then the scanned example can be worked out. The date code of HH would give a manufacturing date of August 1957.


Acknowledgement



This note about Hemmi date codes was assembled from a range of sources but particular mention should be made for information researched and collated by Ted Hume and Paul Ross and available in the Slide Rule Archives section on Walter Shawlee's site The Slide Rule Universe.


Last updated: 2002-08-17 16:15 AEST
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