Citizen’s Chronometer Standards

I finally feel confident enough to publish a reference page on the standards Citizen used for their mechanical and electro-mechanical chronometers in the 1960s and 1970s. After a fair bit of research  I think I’ve reached the right conclusions, but I welcome any comments / observations especially if there’s anything you think I have missed or got wrong!

Page is here:



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2 Responses to Citizen’s Chronometer Standards

  1. chuck says:

    Your summary of Citizen chronometer standards is fascinating. Congratulations!
    However, the protocols raise a question that might be relevant to ordinary watch owners. Namely, when, how often and to what extent are test watches wound–and for automatic only pieces, how? I can’t help but feel these are worth knowing…

    • sweephand says:

      Hi Chuck – thanks for your kind comment. And a good question! I found this about the post-1973 COSC methods:

      Each uncased movement is individually tested for fifteen days, in five positions, at three different temperatures. The movements are fitted with a seconds hand and the automatic winding mechanisms are disengaged for the tests. Measurements are made daily with the aid of cameras


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