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Understanding What a Certified Chronometer Watch Is And How It Is Rated

With summer here and everyone focused on sports watches and timepieces that can keep up with their rugged, active lifestyles, it's a good time to take a closeup look at what it means when a watch is a certified chronometer.

Chronometer roots date back to the 18th century when ships at sea were running aground because they had no way to determine longitude. A race was on amongst the seafaring countries to develop an onboard instrument that could keep accurate time and calculate longitude. When the first such pieces were made for ships they were referred to as chronometers and were considered the most rugged, durable timepieces to date.

Chronometer

Today, many watch brands insist that their high-precision watches house a movement that can keep up with the active pace of today's individuals. This means putting them through stringent testing in different positions and in all sorts of conditions (water, weather, humidity, pressure, etc.).

Generally, a chronometer is rated under laboratory conditions in a specified testing institute and is then certified as having passed those tests within certain ranges of accuracy and precision. There are several chronometer testing institutes around the world (Germany has the Glashutte Observatory in Saxony; France has the Observatory at Besancon), and some brands test their watches in-house and certify them accordingly.

The well known testing institute for Swiss watchmaking is the Controle Officiale Suisse des Chronometres – or C.O.S.C. There are three different COSC laboratory testing facilities in Switzerland: Biel/Bienne, Geneva, LeLocle, but they all use the same guidelines and criteria.

ISO 3159 Criteria

Each watch tested must comply with ISO 3159 standards after being tested for five to 15 days in five positions at several different temperatures. Measurements are made daily via cameras and advanced equipment based on comparisons with two independent atomic clocks. After testing, watches must meet an average daily rate criteria of -4/+6 seconds; a mean variation in rate of 2 seconds; a thermal variation of + or – 0.6; and more.

Certified COSC chronometers

Certified COSC chronometers have a serial number engraved on the movement and are sold with a certificate. Because of the rigorous testing and high standards, just about 3 percent of all Swiss watches produced are COSC-certified chronometers.

Stop in any time to see the chronometer watches we carry.