Zenith EL PRIMERO 21 9004 Mode D'emploi page 11

If you do not wear your watch during the night, turn the crown a
few times the following morning before you put it on.
Having been wound, the power reserve of your watch is
around 50 hours, but this does not appear on the dial. Only the
chronograph power reserve appears on the dial of your watch.
CHRONOMETER CERTIFICATION
The El Primero 9004 movement has been certified as a
chronometer by TIMELAB in Geneva. It has been tested and
successfully meets the requirements set by the ISO3159
standard.
A chronometer is a device that measures time to the highest
accuracy, and can be adjusted to different positions and under
a range of temperatures.
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