What is chronometer
A chronometer is an extremely accurate watch or clock. It takes its name from the Greek words (chronos + metron) meaning to measure time. A Swiss chronometer is a watch, usually mechanical, whose precision has been tested and verified by an official Swiss watch testing bureau. The watch comes with a ratings certificate issued by the institute. The chronometer designation is a badge of honor, proof that the watch is of superior quality.
How to earn the title of chronometer
The watch’s movement must pass a battery of severe tests conducted for 15 days and nights. The movement’s accuracy is checked in five different positions and at various temperatures which simulate conditions under which the watch will be worn.
What Tests should a watch go through to have the title
COSC conducts elaborate precision tests on the movements using cameras and computers, which analyze the data. COSC performs seven different tests. Failure to meet the minimum standard in any one of the tests means that a movement is rejected. The tests are complicated. Here is an attempt at a simple summary:
Test 1 : Mean Daily Rate: After 10 days of tests, the mean daily rate of the movement must be within the range of -4 to +6 seconds per day. COSC determines the mean daily rate by subtracting the time indicated by the movement 24 hours earlier from the time indicated on the day of observation.
Test 2 : Mean Variation in Rates: COSC observes the movement’s rate in five different positions (two horizontal, three vertical) each day over 10 days for a total of 50 rates. The mean variation in rates can be no more than 2 seconds.
Test 3 : Greatest Variation in Rates: The greatest of the five variations in rates in the five positions can be no more than 5 seconds per day.
Test 4 : Horizontal and Vertical Difference: COSC subtracts the average of the rates in the vertical position (on the first and second days) from the average of the rates in the horizontal position (on the ninth and tenth days). The difference must be no more than -6 to +8 seconds.
Test 5 : Greatest Deviation in Rates: The difference between the greatest daily rate and the mean daily test rate can be no more than 10 seconds per day.
Test 6 : Rate Variation Due to Temperature: COSC tests the movement’s rate at 8 degrees Celsius (46 degrees Fahrenheit) and at 38 degrees C (100 degrees F). It subtracts the cold temperature rate from the hot temperature rate and divides by 30. The variation must be no more than 0.6 seconds per day.
Test 7 : Resumption of the rate: This is obtained by subtracting the average mean daily rate of the first two days of testing from the mean daily rate of the last test day. The resumption of rate can be no more than 5 seconds. Simple, isn’t it? If a movement meets the standards, COSC issues a certificate designating it as a "chronometer."
Who conducts the tests
The Swiss Official Chronometer Control (Controle Officiel Suisse des Chronometeres, or COSC, in French). COSC is an independent association governed by the Swiss Civil Code.
Watch companies desiring the chronometer designation on their best pieces send movements to COSC. (COSC tests uncased movements; the companies case the movements after the tests.) COSC issues a performance certificate for each timepiece which successfully passes the tests.
There are three COSC centers in Switzerland where watch companies send movements to be tested—in Geneva, Bienne and Le Locle.
Switzerland has been officially testing chronometers since 1878. COSC as it exists today was founded in 1973.
What is the difference between a chronometer and a chronograph
The terms sound similar but they have nothing to do with each other. A chronometer, as we have seen, is a superior timekeeper. A chronograph is a watch with a stopwatch function.
