Compensation of rate variation in a watch

A method for compensating a rate of a movement (3) as a function of the temperature of a water-resistant watch (1), wherein a water-resistant case (2) of the water-resistant watch (1) contains the movement (3) including an oscillator (4), said case (2) containing, on leaving a factory after an initial rate setting, an internal volume V occupied by n moles of a gas of constant R substantially observing the ideal gas law, wherein a pressure coefficient Cp of said movement (3) is determined in the factory by measurement and/or calculation, defining a relatively linear variation of the rate of said movement (3) as a function of a pressure P of said gas, wherein a value of a humidity coefficient Ch of said movement (3) is determined in the factory after measurement and/or calculation, defining a maximum relatively linear variation of the rate of said movement (3) as a function of a humidity H in said movement (3), wherein an optimal value Cto of a thermal coefficient Ct of said oscillator (4) is calculated defining a relatively linear variation of the rate of said oscillation (4) as a function of a temperature T, said optimal value Cto being intended to compensate pressure and humidity deviations according to the formula:

• Cto=−[Cp*(n*R)/V]−[(Ch*H)/T],
• and wherein,
• either for an after-sales application or when casing up in the factory, said watch (1) is equipped with compensation means (10) arranged to vary, inside said case (2), the pressure P and/or a nature of the gas and a constant R and/or a quantity of gas and a number of moles n and/or the temperature T,
• or for a preparation in the factory, the thermal coefficient of an elastic return means included in said oscillator (4) is modified by modifying an oxide layer thickness and/or applying a coating and/or by local ablation, and/or the number of moles of gas in said watch and/or the nature of the gas in the watch are modified, and/or the internal volume of said case (2) is modified.