The "Chronometer" certification guarantees the high accuracy of a watch or a movement.
The tests run by the COSC include the verification of the engraved number on the watch movement and controls in a testing environment. Each movement is individually tested following a strict procedure that lasts several days in five positions and at different temperatures (8°C, 23°C and 38°C). Over 15 days, the movements go though daily controls. Every day - including Saturday and Sunday - the instruments are measured and wound. If it meets the standards, the movement is "Chronometer" certified.