Adjusted to five positions – nothing to do with Playboy this time!

These days it may seem common that a watch is referred to as a chronometer. After all, every Breitling and most ROLEX carry this certification. But what does it actually mean, what standard does a watch have to meet before its labelled a “Chronometer” ( A watch shown to have met strict time keeping standards as described by the COSC or Controle Officiel Suisse des Chronometres or other official body ISO 3159) Out of the yearly Swiss made watch production only about 4% of mechanical watches are certified chronometers while approximately 1/3 of 1% are Quartz. In total around 60 manufacturers submit movements for testing, with ROLEX being by far the biggest by volume. So this certification is actually very prestigious and desirable. In very basic terms this certification means the watch can keep time to within -4 to +6 seconds a day, if its an automatic. Or +/-0.07 seconds for Quartz. Now in addition to the basic daily rate standards, each movement is tested for accuracy in five different physical positions. Three vertical and two horizontal. This is done at different temperatures as well. In all seven different tests are performed before the movement can be certified as a chronometer. 1.Mean Daily Rate: After 10 days of tests, the mean daily rate of the movement must be within the range of -4 to +6 seconds per day. COSC determines the mean daily rate by subtracting the time indicated by the movement 24 hours earlier from the time indicated on the day of observation. 2.Mean Variation in Rates: COSC observes the movement’s rate in five different positions (two horizontal, three vertical) each day over 10 days for a total of 50 rates. The mean variation in rates can be no more than 2 seconds. 3.Greatest Variation in Rates: The greatest of the five variations in rates in the five positions can be no more than 5 seconds per day. 4.Horizontal and Vertical Difference: COSC subtracts the average of the rates in the vertical position (on the first and second days) from the average of the rates in the horizontal position (on the ninth and tenth days). The difference must be no more than -6 to +8 seconds. 5.Greatest Deviation in Rates: The difference between the greatest daily rate and the mean daily test rate can be no more than 10 seconds per day. 6.Rate Variation Due to Temperature: COSC tests the movement’s rate at 8 degrees Celsius (46 degrees Fahrenheit) and at 38 degrees C (100 degrees F). It subtracts the cold temperature rate from the hot temperature rate and divides by 30. The variation must be no more than 0.6 seconds per day. 7.Resumption of the rate: This is obtained by subtracting the average mean daily rate of the first two days of testing from the mean daily rate of the last test day. The resumption of rate can be no more than 5 seconds. If the movement passes all these tests it is deemed to be worthy of the Chronometer certification – and a unique serial number is engraved onto the movement linking it to the proof of that testing. Some manufacturers supply the COSC certificate to the customer, eg Panerai and Breitling while others do not, Rolex and Omega among others. In real terms this certification means that you are buying a watch that has met the absolute highest standards of modern watchmaking and that is among the best of its type in the world.see more repliche rolex and vacheron