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.

I use the words "model number" and "catalog number" interchangeably for Frederick Post brand items.

was founded April 15, 1895 but no Hemmi slide rules from before about 1913 are known.

This cursor may not be authentic Hemmi but the rule it came on is consistent with a date of about 1913. The plain version (non magnifying, non decimal-indicating) appears only in the 1913 Tamaya catalog.

Magnifiying and decimal-indicating versions (but not plain versions) appear in the 1914 Hughes-Owens and the 1919 Tamaya catalogs.

Some Hemmi slide rules that clearly should have date codes, don’t. The absence of a patent number provides no information about the date of manufacture; slide rules intended for sale in Japan never carried US or British patent numbers--no matter when they were made.

Cursors are not reliable indicators of the age of slide rules; too many broken cursors were replaced with newer models.

Hemmi introduced a new model numbering system between 19.

(I have not been able to narrow the date.) Rules with model numbers 1-18 date from before this changeover, rules with model numbers 20 and above were made after the changeover.

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.