Step
01
Day 01
RIGOR FROM THE VERY BEGINNING
Reception of the movements
Verification of the engraving numbers
Placement of the movement in a 5-slot clasp
The parts remain in an enclosure at 23°C for 12 hours
"Chronometer Certified"
A hallmark of quality and precision
Being certified by the COSC means belonging to the elite. It is the recognition of a flawless quality system and proof that the brand has embraced a “chronometer mindset” at every stage of production, from research and development through to precision testing.
The “chronometer certified” label
This title is certified by an official, neutral authority in accordance with the ISO 3159 standard. In Switzerland, each certified chronometer is identified by a unique number engraved on its movement and is accompanied by a certificate issued by COSC. Many brands also choose to display the designation “Chronometer Certified” directly on the watch.
Four types of timekeeping instruments
The COSC mainly certifies mechanical wristwatches, but also pocket watches, fixed-time devices and quartz wristwatches.
To obtain “Chronometer Certified” certification, wristwatch movements must meet the criteria set out in ISO 3159, which define a wristwatch with a balance-spring oscillator.
Movements in other categories, including quartz watches, are based on in-house specifications inspired by ISO 3159, but adapted to the specific features of each instrument.
The stages of certification
Each movement undergoes the most stringent tests, integrating temperature and position variations, over 12 to 20 days, depending on its type, to ensure optimal precision.
Understanding certification
Step
02
Days 02 to 10
TIME MEASUREMENT
Time measurement
Winding
Placement in position
These operations are carried out in 24-hour cycles
The position changes daily: 6 o’clock, 3 o’clock, 9 o’clock, then the dial facing up and finally the dial facing down
Step
03
Days 11 to 13
A QUEST FOR EXCELLENCE
Time measurement
Winding
Placement of movements dial up
Successively placed in chambers at 8°, 23°, then 38° for 24 hours
Step
04
Days 14 to 15
THE LAST MEASUREMENT
Time measurement and winding
Positioning of movements at 6 o'clock
Step
05
Days 16 to 20
METICULOUS ANALYSIS OF THE RESULTS
Assessment of compliance with the 7 certification criteria
Creation of the “COSC-certified chronometer” certificate
Returning the movements to clients
Our 7 criteria for certification
To qualify as a Certified Chronometer, movements must meet 7 criteria. At the end of all the tests, a calculation is performed to verify that these criteria have been met:
Average daily rate
Rate variation as a function of temperature
Rate resumption
Greatest difference in rates
Difference between rates in horizontal and vertical positions of the watch
Greatest variation in rates
Mean rate variation
THE CERTIFICATION
Discover "Excellence Chronometer Certified"
Discover the "COSC Excellence Chronometer" certification, which pushes the traditional boundaries of watch certification. As the world changes, so do the requirements for precision and robustness.
La Certification
FAQ
What is the COSC standard for automatic (mechanical) watches?
The COSC standard for automatic (mechanical) watches is based on the ISO 3159 standard, which defines the criteria for a balance spring oscillator wristwatch chronometer. To achieve the COSC certification, a mechanical watch must meet several stringent criteria over a testing period of 15 days. During this time, the watch is tested in five different positions and at three different temperatures (8°, 23°, and 38°C). The key criteria include:
Average Daily Rate: The watch must maintain an average daily rate between -4 and +6 seconds per day.
Mean Variation in Rates: The consistency of the rate over the testing period.
Greatest Variation in Rates: The largest difference in rate observed during the tests.
Difference Between Rates in Horizontal and Vertical Positions: Ensures the watch performs consistently regardless of its orientation.
Largest Variation in Rates: The maximum deviation in rate observed.
Variation in Rate Depending on Temperature: The watch's ability to maintain accuracy across different temperatures.
Rate Resumption: The ability of the watch to return to its original rate after being subjected to different conditions.
Only watches that meet all these criteria are awarded the official chronometer certificate, signifying their high precision and reliability
What information can the buyer of a chronometer-certified watch obtain from the COSC?
None. The COSC is the repository of analytical results that belong to its customers (the watchmaking brands). It does not have the authority to disclose information to anyone other than the legitimate owners of those results. The buyer should contact the head office of the brand to which the chronometer belongs.
Is every chronometer sold with a certificate from the COSC?
No. Documents issued by the COSC are optional. It is for the brands themselves, and only them, to decide whether or not to communicate the results obtained during certification of the movement or watch by the COSC.
How long is the chronometer certification valid?
The chronometer designation can be compared to a university degree. At a given moment in life, the candidate proved, on the basis of an examination, that they have met all of the performance criteria that allowed them to merit the designation. Just as is the case for a graduate, this designation is acquired for life, even if one's performance is likely to change somewhat over time.