A chronometerChronometer A chronometer watch movement is a high-precision movement that has been certified by an official organization, such as the Swiss Official Chronometer Testing Institute (COSC) or other similar bodies, as meeting certain standards of accuracy and performance. These standards include requirements for the rate of the watch, its resistance to temperature and other environmental factors, and its power reserve. Chronometer watches are tested for several days, in different positions, and at different temperatures to ensure their precision. [Learn More] watch movement is a high-precision movement that has been certified by an official organization, such as the Swiss Official Chronometer Testing Institute (COSC) or other similar bodies, as meeting certain standards of accuracy and performance. These standards include requirements for the rate of the watch, its resistance to temperature and other environmental factors, and its power reserveRéserve de marche Also known as Power Reserve. A watch's power reserve refers to the amount of time a mechanical watch can run without being wound. The power reserve of a mechanical watch can vary depending on the size of the mainspring, the efficiency of the gear train, and the rate at which the mainspring releases energy. If a watch has a Power Reserve 'complication' it simply means that the status of the power reserve can be seen on the watch itself (either on the dial or movement side of the watch). [Learn More]. Chronometer watches are tested for several days, in different positions, and at different temperatures to ensure their precision.