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JIS B 7025 in its 1995 edition is the current Japanese standard for 'accuracy indication', i.e. how makers may advertise the accuracy of quartz watches (and clocks).
First the good news
At the tier of 'annual accuracy', the JIS mandates that manufacturers measure three things:
1) Temperature variation Vt
2) Aging variation Va
3) Battery voltage drop variation Ve
These are added together and…
The 1995 Japanese Industrial Standard for HAQ and its fatal flaw