Real world expectations of a COSC movement
With the new 50th Anniversary SUB300 just about ready to ship, I wanted to take some time to talk about the COSC movement powering the SUB300, and what can be expected from it.
First let me describe what COSC certification is and is not:
The COSC certifies that the movement has been adjusted in 5 positions at 3 different temperatures to an average daily rate of −4/+6 seconds per day, under laboratory conditions.
It is very important to understand that the regulation (adjustment) and test was carried out under laboratory conditions uncased and stationary. The COSC certification does not guarantee a long term performance or accuracy, it only certifies that the movement was capable of achieving superlative accuracy results at a given time.
Real world conditions will affect the daily rate in countless ways. Please do not be surprised that your SUB300 may not run at the same rate listed on the COSC certificate every day. There will be fluctuations and deviations from those figures depending on the temperature fluctuations and the amount of wrist/body movement.
We also want to assure customers that if they receive a watch that is not working properly, or at all, we will take care of it as quickly as possible. We did set aside a small number of watches for replacements.
Switzerland’s Contrôle Officiel Suisse des Chronomètres, or COSC, is the best-known watch-certifying organization. The COSC procedure lasts 15 days. Watch companies send their movements to COSC uncased. COSC then assigns each an identification number and its employees apply a generic dial with reference points that help an optical sensor track the watch’s seconds hand. Each movement is wound mechanically (automatic movements must remain rotor-less), then given a rest period of 24 hours before testing. The optical sensor reads the time off the dial daily. This reading is logged to a server controlled by two atomic clocks, which provide a timing standard. During the first 10 days, the movement is tested in five positions, each for 48 hours: crown left, crown up, crown down, dial up and dial down. Movements are kept at a temperature of 23 degrees Cº, or 73.4 degrees Fº, during this period. If a movement has a chronograph function, it is activated on day 10 to check its effect on timekeeping. On days 11 through 13, the temperature is lowered to eight degrees Cº (46.4 degrees Fº), then returned to 23 degrees Cº, then raised to 38 degrees Cº (100.4 degrees Fº). For the last two days, the temperature is brought back down to 23 degrees Cº and the movement is returned to its original position with crown facing left.