A watch with a movement that has demonstrated outstanding accuracy by passing the tests of the COSC (the official Swiss Chronometer Control Office). Each movement is individually checked in five positions: crown left, crown right, crown up and dial up. Its accuracy must remain between -4 and +6 seconds over 24 hours, and the deviation may not vary by more than 5 seconds during the 15-day test period. Testing is done at 8°C, 23°C and 38°C. Only watches with movements that have passed this testing process are officially certified as chronometers. In general, the word "Chronometer" appears on the dial.