COSC measurement methods
To our knowledge, the BOs are the only laboratories in the world to apply this standard on an industrial scale and to deliver more than 1,000,000 official chronometer certificates per year. Nonetheless, this represents only 3% of Swiss watch production, a proportion that underscores the exceptional nature of a chronometer.

In doing so, they rigorously apply the testing conditions laid down by the norm.

It is vital to recall the fact that these tests bear absolutely no relation to a simulation of watch behaviour and performance when worn.

These are static tests applied in laboratory conditions to movements and not to finished watches.

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The results provide a "photographic" image of the rate of a movement at a given moment and certify its intrinsic position.

Nonetheless, due to their severity, these tests are highly selective and only extremely high-quality movements can hope to pass them.
This is therefore an examination based on excellence, even if the behaviour of the movements that are granted certification is still directly dependent on the wearers themselves.
To earn chronometer certification, a movement must not only be made from the highest-quality components, but also the object of special care on the part of the finest watchmakers and timers during assembly.
It is thus a product with extremely high value added and therefore stands out quite clearly from standard quality watch production.