What is a Chronometer
rating on a watch?
Simply put, a Chronometer
is a rating for a watch in regards to its accuracy. However a Chronometer
rating not only applies to wrist watches; it can also apply to pocket watches,
marine and observatory chronometers and various other scientific timing
equipment.
The history of the Chronometer rating.
For a wrist watch to
be certified as a “Chronometer”, it must first go the non-profit company in
Switzerland called the COSC which stands for Contrôle Officiel Suisse des
Chronomètres.
The history of the COSC
goes back to the end of the 19th Century, and was founded by five
watchmaking states of Switzerland: Geneva, Bern, Neuchâtel, Vaud and Solothurn,
together with the Federation of the Swiss Watch Industry (FHS).
Originally, a
chronometer was used as a timekeeper that was precise enough to be used as a
portable time standard, usually in order to determine longitude by means of
celestial navigation
Today there are 3 laboratories
which now test the movements submitted by watch companies to be certified as a chronometer,
which are in Geneva, Bienne and Le Locle.
What is involved in rating a watch as a Chronometer?
A watch movement isn’t
simply submitted to the COSC for testing, nor is one watch movement
representing multiple movements from the one watch company.
Each watch movement
is individually tested, and if the watch movement passes the strict criteria defined
by the COSC, it is then given an individual officially recorded serial number and
certificate.
If the movement is
mechanical, i.e. not a quartz powered movement, the movement is then tested
over 15 days, in 5 different positions, and at 3 different temperatures, and
during this time the movement must not gain more than 6 seconds, and not lose
more than 4 seconds per day.
The following graph
shows the different temperature and positions that the movement is placed in.
Day Temperature Position
0 23°C 6 o'clock
up
1 23°C 6
o'clock up
2 23°C 6
o'clock up
3 23°C 3
o'clock up
4 23°C 3
o'clock up
5 23°C 9
o'clock up
6 23°C 9
o'clock up
7 23°C Dial
down
8 23°C Dial
down
9 23°C Dial
up
10 23°C Dial
up
11 8°C Dial up
12 23°C Dial
up
13 38°C Dial up
14 23°C 6
o'clock up
15 23°C 6
o'clock up
Once the individual watch movement has passed this criteria,
the word "Chronometer" can then be written on the dial.
Why are some Swiss watches not Certified?
Each year
approximately 1,000,000 watches are sent to the COSC to be certified as a
Chronometer. This sounds like a very large number – which in itself it is,
however this number represents around 3% of the annual production of watches.
Rolex is widely known
as the watch company that supplies the most watches to the COSC to be
certified. Each year approximately 83% of the watches certified COSC come from
the Rolex factory.
It should be noted
that not all of the watch companies send their watches to get certified. Some
very well and very highly respected firms such as Jaeger-LeCoultre, IWC, Audemars
Piguet, Breguet, Piaget and A. Lange & Söhne are among the expensive brands
that do not submit their movements to the COSC.