Held under the auspices of the Watchmaking Museum at the Chateau des Monts in Le Locle, the International Chronometry Competition is held every two years and is open both to companies (brands, movement manufacturers and independents) and schools. Its tests are based on the ISO standards used for the definitions of chronometer (ISO 3159) and for resistance to magnetic fields (ISO 764). The competition has developed its own testing procedure for magnetic shocks (see box).

The watches are tested according to the following procedure:

1. All the watches are received at the Watchmaking Museum in Le Locle
2. The watches are tested for 16 days at the Besançon observatory in France accordance with the requirements of ISO 3159 (chronometer)
3. They are then transferred to the COSC office in Bienne, Switzerland, where they undergo another 16 days of chronometer testing
4. Tests for resistance to magnetic fields and shocks are carried out at the Haute Ecole Arc. The tests for resistance to magnetic fields are carried out in accordance with the ISO 764 standard, while those for shock resistance are the subject of the school’s own special tests, which are carried out using a modified robot that exposes the watch head to 150 shocks at an intensity of 150g as follows: 50 shocks on the 3 o’clock to 9 o’clock axis, 50 on the 6 o’clock to 12 o’clock axis and 50 shocks perpendicular to the dial (25 in each direction).
5. After these tests, the watches once again undergo the 16 days of chronometer testing, where any adverse effects from the shock or magnetism tests will make themselves known.

The specially modified robot at the Haute Ecole Arc in Le Locle that is used for the shock-resistance testing in the International Chronometry Competition

Each watch is then given a score out of 1000 that is calculated using the following formula, which will determine its overall rating in the competition:

N = 1000 – [12.5*M_moy + 55*V_moy + 45*V_moyc + 20*V_max + (100/3)*D + 10*P + 500*C +10*R]

The variables are taken from the COSC criteria and the fixed integers are weightings that are applied to each value, thus:

M_moy = Mean daily rate (weighting: 12.5)
V_moy = Mean variation in rates in position (weighting: 55)
V_moyc = Mean variation in daily rate between positions (weighting: 45)
V_max = Greatest variation in rates (weighting: 20)
D = Difference between rates in horizontal and vertical positions (weighting: 100/3)
P = Largest variation in rates (weighting: 10)
C = Thermal variation (weighting: 500)
R = Rate resumption (weighting: 10)

There are no subjective criteria, so the watch with the highest score wins.