Over the centuries, as clocks evolved and wristwatches came into being, the concept of conquering the feat of chronometer status for the wrist remained important. Today, a wristwatch can achieve chronometer status if the movement inside it has been certified according to strict standards by an outside observatory.
There are chronometer testing facilities in Besancon, France, in the Saxony region of Germany, in Japan and other places around the world, including several in Switzerland. Chronometer criteria can vary slightly from each observatory. For Swiss watches, the most well-known and prestigious observatory is the Controle Officiel Suisse des Chronometers (COSC), with three locations in Switzerland. When collectors refer to their watches as being “COSC certified”, it means the chronometer certification comes from the Controle Officiel Suisse des Chronometers.
Focusing on the standards of the COSC, certification criteria is based on ISO 3159 standards. To gain chronometer certification from COSC, it is tested for 15 days in five different positions and in multiple circumstances such as extreme temperatures, humidity, pressure and more. Measurements are taken daily and are compared with two independent atomic clocks.
During testing, watches are placed in various positions: 3 o’clock, 6 o’clock, 9 o’clock, dial on top, dial on the bottom. Each watch remains in each position and given temperature for 24 hours. Each day, the watches are removed for a brief moment to take measurements.
Only watches that meet the precision criteria can be granted an official chronometer certificate. The mechanical watch may not have a daily variation of more than -4 or +6 seconds per day. Only approximately 3% of watches produced in Switzerland will make their way through COSC’s certification process. The chronometer certification ensures that each individual mechanical watch tested is durable and incredibly precise.
When watch brands utilize a chronometer movement inside a watch, most will indicate “chronometer” stamped on the dial. After all, they have conquered a lot to achieve this status.