Method for adjusting the chronometry of a timepiece movement intended to operate in a low-pressure atmosphere

A method for regulating time-keeping of a mechanical timepiece movement intended to operate in a low-pressure atmosphere, includes the successive steps of: placing the movement in a low-pressure atmosphere pre-established for normal operation of the movement; measuring the gain or recoil (typically a gain + P) of the time-keeping precision of the movement at this low pressure; returning the movement to ambient atmospheric pressure; at the ambient atmospheric pressure, regulating the movement to compensate for the previously measured gain or recoil; and returning the movement to the low-pressure atmosphere pre-established for normal operation of the movement.