Citizen’s 1962 31j Chronometer – Accuracy Standards

Further to my last post about Bill’s Chronometer, and Marko’s comments about the Japanese certificate, here are some more scans of Citizen’s standards for this watch in the 1960s. First is a certificate showing the standards that had been met:

Next is the Rating Certificate which shows how the watch being tested performed against these standards – as you can see it achieved significantly better results:

Note that the ‘mean daily rate’ variation was less than a second 🙂

The date at the bottom of the above certificate is in the ‘Showa’ period, and equates to 29th September 1965.

The next document shows results against the different tests:

Finally, this scan, although in Japanese, shows how the standards were changed from 1955 to 1961:

The Swiss COSC chronometer standard from 1961 to 1973 required a mean daily rate in five positions of -1/+10, so Citizen were using the same approach. As far as I know (unlike Seiko) they never entered any movements in the COSC competitions in the 1960s. The certificates in these scans look to be Citizen’s own – in 1968 the Japan Chronometer Inspection Institute was founded, but I’ve not seen any standards / certificates published by the JCII. I would assume that they at least matched the Swiss standards.

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