The Swiss Offical Chronometer Control is certified by the Swiss official observatory testing organization (referred to as C.O.S.C.) for watch accuracy.
Qualified watches are often referred to as Chronometer-Observatory tables. The word Chronometer comes from the synthesis of two Greek words: Khronos (time), Metron (calculation, measurement). C.O.S.C. have a test center in three locations in Geneva, Belgium, Bill and La Chaux-off. In the total number of watches in the test, about 2% -3% will be eliminated. As the test is only one test, so even with the same paragraph of the two tables, the test results in the figures may also have a number of gaps.
Observatory certification is for the mechanical watch movement and carry out the certification, was sent to the movement, will be in the Swiss official observatory test organization for 16 days 24 hours without interruption to accept three kinds of temperature (- 8,23 and 38 degrees Celsius ) And five locations. Including the average daily speed, speed changes, speed differences, sustained speed and many other tests, through all the detection of the movement, was awarded the "Observatory table" movement, engraved in the dial "Chronometer" words. Day to Taiwan standard is -4s ~ +6 s.
Rolex is cosc certified the largest watch provider. They almost all the mechanical movement to the cosc, in 2001 they received 761601 Observatory certificate, an increase of 20% over 2000. "All Rolex mechanical watches have passed the Observatory certification," at the Rolex headquarters in Geneva with such rumors.