What criteria define a watch certified a Chronometer?
The designation chronometer is registered and used only if an independent inspection authority has tested the movement of a watch. In Switzerland, this inspection authority is better known as the Swiss Official Chronometer Testing Institute or C.O.S.C. The C.O.S.C. tests the movements submitted to it for their accuracy over a period of 15 days: the first 10 days at room temperature and for the last 5 days at a range of different temperatures. If the measured timekeeping deviations lie within the set tolerances, usually of 4/6+ seconds per day, or a precision of 99.99%, the highest precision attainable by a mechanical movement, only then is a certificate Swiss Official Chronometer issued for the movement.
