A chronometer is an extremely accurate watch or clock. The movement has been tested for accuracy in 5 different positions and at various temperatures which simulate Arctic and Tropical conditions under which the watch will be worn. Most chronometers are mechanical watches because there is little need to prove a quartz watches accuracy, as electronic quartz technology is by definition an ultra-precise form of time keeping. The tests are conducted by the Swiss Official Chronometer Control (Controle Officiel Suisse des Chronometres, or COSC). COSC is an independent association governed by Swiss Avil Code. The tests are very involved and elaborate, cameras and computers are used to analyse the data.

Test 1
Mean Daily Rate
The timekeeping must be between -4 to +6 seconds a day for 10 days.
Test 2
Mean Variation Rates
Timed over 10 days in 5 different positions the mean variation in rates can be no more than 2 seconds.
Test 3
Greatest Variation
Cannot vary more than 5 seconds a day in any position.
Test 4
Horizontal and Vertical Difference
The average timekeeping over 2 days in the vertical position is subtracted from the average timekeeping in the horizontal position. The difference must be no more than -6 to +8 seconds.
Test 5
The Greatest Deviation in Rates
The difference between the greatest daily rate and the mean daily rate can be no more than 10 seconds a day.
Test 6
Temperature Variation Rate
The variation between timekeeping at 8 degrees Celsius and at 38 degrees Celsius must be no more than 0.6 seconds a day.
Test 7
Resumption of the Rate
The resumption must be no more than 5 seconds, when the average mean daily rate of the first two days is subtracted from the mean daily rate of the last day.


INVICTA, 1960's
INVICTA, 1960's
INVICTA, 1960's

Servicing Chronometers

Individual certificate by the Swiss B.O.

Watches I have repaired, restored and overhauled have obtained chronometer certificates with mention of "very good rate results". Servicing a chronometer is different from overhauling a normal timepiece. More time is spent in adjusting the timekeeping than the stripping and re-assembly. All the timepieces marked chronometer have the potential of becoming excellent timekeepers.

JAEGER-LECOULTRE, model 'Geophysic',1958
JAEGER-LECOULTRE, model 'Geophysic',1958
JAEGER-LECOULTRE, model 'Geophysic',1958
JAEGER-LECOULTRE, model 'Geophysic',1958

-   The Omega Constellation Chronometer   -

The 1st constellation model was introduced in 1952. The automatic movement calibre 354-28-10, seventeen jewels, self winding mechanism with rotor winding in one direction with bumper springs. These watches are now known as Bumpers. All constellations have the observatory under the night sky emblem on the case back.

Omega had 13,952 watches certified as chronometers in 1952, in 1963 103,040 watches certified and by 1969 194,580. By 1972 two million certificates had been issued.

These were golden years for Omega chronometer production - mass production of an extremely fine timekeeper along with a distinctive style, making these watches into classic timepieces. In 1956 the Bumper was replaced with Calibre 500 incorporating the central rotor. Three years later calibres 551 and 561 took over.

Before the crash of the Swiss Watch Industry at the beginning of the 1970's, the Omega Collection consisted of 2,000 different case styles, a large number of these constellations.

Financial problems led Omega to cut back the number of models and limit the production of mechanical watches. This, in my opinion, was the end of the golden years of wrist watch manufacturing.

I usually have a small number of constellations for sale. Please click here to view what I have in stock.

On a personal note, after serving my apprenticeship with Girard Perregaux watches, I went to work for the Omega watch company. The Omega constellations from this period before 1970 are, in my opinion, the best high volume watches ever produced. The reliability, finish of the movement, and the distinctive styling of the cases is unsurpassed.

Chronometer wristwatch by OMEGA, model 'Constellation', 1963