Have you ever wondered what exactly the COSC Certification for mechanical watches entails? I have – So I looked it up.

There are three labs all located in Switzerland that do the COSC certification: One in Geneve, one in Le Locle, and one in Biel/Bienne. The entire testing process takes 15 days, and the watches are tested in five positions. The watches are tested as movement only, and do not come with hands or anything. Automatic movements have the rotors detached during testing and three temperatures are tested as well. 23 Degrees Celcius is the main temperature tested.

NOTE: I have received conflicting information as to whether the second hand attachement and rotor removal is done by the COSC or by the company sending the movements in. Initially I had read that it was done by the company sending it in and not the COSC, but have not been able to find reference to that anymore. Any information would be great!

15 Days for Mechanical watches

Day 1 : 23 Degrees Celcius – Vertical – 6 o’clock up
Day 2 : 23 Degrees Celcius – Vertical – 6 o’clock up

Day 3 : 23 Degrees Celcius – Vertical – 3 o’clock up
Day 4 : 23 Degrees Celcius – Vertical – 3 o’clock up

Day 5 : 23 Degrees Celcius – Vertical – 9 o’clock up
Day 6 : 23 Degrees Celcius – Vertical – 9 o’clock up

Day 7 : 23 Degrees Celcius – Horizontal – Dial Down
Day 8 : 23 Degrees Celcius – Horizontal – Dial Down

Day 9 : 23 Degrees Celcius – Horizontal – Dial Up
Day 10 : 23 Degrees Celcius – Horizontal – Dial Up

Day 11 : 8 Degrees Celcius – Horizontal – Dial Up
Day 12 : 23 Degrees Celcius – Horizontal – Dial Up
Day 13 : 38 Degrees Celcius – Horizontal – Dial Up

Day 14 : 23 Degrees Celcius – Vertical – 6 o’clock up
Day 15 : 23 Degrees Celcius – Vertical – 6 o’clock up

Seven things tested for Mechanical watches

  1. Over the first 10 Days the average daily rate must be within -4/+6 seconds
  2. Mean variation in rate cannot be higher than 2 seconds in any single position
  3. Greatest variation in rate between any 2 days cannot be more than 5 seconds in any single position
  4. The difference of the rates in the vertical and horizontal positions cannot be more than -6/+8 seconds
  5. The difference between the main daily rate and any individual rate cannot be more than 10 seconds
  6. Variation in temperature cannot be more than 0.6seconds per degree
  7. Difference between the mean daily rate of the first two dates compared with the the last two dates cannot be more than 5 seconds.

Many brands do not submit to COSC, and feel that their watches are good enough on their own merit. This may be true, but COSC does have its place, and at least in my opinion, it is not a gimmick. It provides the end-user with a third-party certification that their watch is accurate. That is nice to have, though, not necessary in most cases.

Quartz watches have a different set of parameters that must be met.. perhaps we’ll discuss those in a different post 🙂