Watchmaking certification or the quest for ultimate precision

Watchmaking certification or the quest for ultimate precision

COSC: what lies behind these four letters? An international symbol of Swiss watchmaking precision, this label (standing for the French version of the Swiss Official Chronometer Testing Institute) certifies the precision of Swiss watches on demand.

What would be the point of watch if it were not accurate? In this respect, certain Maisons are determined to prove that their mechanical gems tolerate nothing less than excellence. To assist them in this quest, they can choose to work with the Swiss Official Chronometer Testing Institute, a venerable institution founded in 1876. As a neutral and independent body, the role of the COSC is to deliver certification of chronometric precision based on an international norm stipulating a test protocol lasting 15 days and relating to seven different criteria. For a mechanical movement, the results must show a variation in rate falling within a range of -4 to +6 seconds a day. If such is the case, it is deemed worthy to enter the peak watchmaking segment of high-precision watches.  Around 1.7 million units per year earn the precious label, corresponding to one-fifth of overall Swiss mechanical watch production. Only a few brands call upon the services of the COSC, headed by a quartet composed of Rolex, Omega, Tissot and Breitling, which together account for more than 80% of watches bearing this certification.


Breitling is one of the world’s only major watch brands to equip all its models with chronometer-certified movements, including that of the Superocean 44 Special Blacksteel designed for abyssal depths with its 1,000-metre guaranteed water resistance.

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A tribute to the very first L.U.C watch launched by Chopard in 1996, this COSC-certified L.U.C XPS 1860 bears the Poinçon de Genève quality hallmark in its rose gold version. A sure token of high-quality construction and finishing.

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With its Calibre 8900 featuring a co-axial escapement, this Omega Seamaster Planet Ocean 600 M is Master Chronometer certified, meaning resistant to magnetic fields equivalent to those of an MRI scan (approx. 15,000 gauss), with a precision tolerance of between 0 to +5 seconds over a 24-hour period.

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The Superlative Chronometer Officially Certified Oyster Perpetual Rolex Deepsea is water-resistant to 3,900m and meets criteria that are even stricter than standard watch industry norms, meaning guaranteed precision with a tolerance of just -2/+2 seconds per day.

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