The Slide Rule Trading Co., Paul Ross

Hemmi Slide Rule Catalogue Raisonne

Dates of Availability

Dates of availability are estimates.  Many models did not appear in the Hemmi catalog until several years after they were officially announced; others never appeared in a Hemmi catalog but dated specimens are known; for some models, all I have is a picture from an auction site.  
Abbreviations used are
Made in Occupied Japan
World War II
End of (Hemmi Slide Rule) Business

Hemmi Date Codes
Most Hemmi slide rules manufactured after 1951 have a code indicating their date of manufacture engraved in very small un-inked letters.  The code is in the form "YM" for bamboo rules or "^YM" for all-plastic rules.  The first letter represents the year with "A" = 1950.  The second letter indicates the month of manufacture with "A" = January.  Thus, "TK" or "^TK" indicates November 1969.  

Usually the date code is near the lower left corner of the rear of the rule but it can be almost anywhere.  Because the letters are small and un-inked the date code can be hard to find--you may need to examine the surface with a magnifying glass in raking light.  

Although the coding system started in 1950, most rules manufactured in 1950 or 1951 do not carry a date code.  The earliest date code of which I am aware is "AL" (December 1950).  Theoretically, the date code system applied through "ZL" (December 1975) but Hemmi became inconsistent about applying them in the last few years of their slide rule business.  "X," "Y," and "Z" date codes are rare.  

For a guide to estimating dates of manufacture of Hemmi slide rules click here.