Timepiece comprising: - a mechanism for indicating a temporal data item, - a mechanical resonator suitable for having an oscillation movement along a given oscillation axis about a neutral position corresponding to the minimum potential energy state thereof, - a maintenance device of the mechanical resonator forming with this mechanical resonator a mechanical oscillator arranged to pace the working of said mechanism, each oscillation of the mechanical resonator having two successive alternations (A1, A2) between two extreme positions, on the oscillation axis, which define the oscillation amplitude of the mechanical oscillator from the neutral position, each alternation having a first half-alternation and a second half-alternation occurring respectively before and after the passage of the mechanical resonator via the neutral position, - a device for regulating the mean frequency of the mechanical oscillator, this regulation device comprising an auxiliary oscillator, an electromechanical device suitable for stopping during an alternation at least momentarily the oscillation movement of the mechanical resonator in the direction of this alternation, and a regulation circuit arranged to be able to generate a control signal intended for the electromechanical device to activate same; the regulation device comprising a sensor, arranged to be able to detect the passage of the mechanical resonator via at least a certain given position on the oscillation axis, and a measuring device arranged to be able to measure, on the basis of a detection signal (S P) supplied by the sensor, a potential time drift of the mechanical oscillator relative to the auxiliary oscillator; the measuring device and the regulation circuit being arranged to be able to determine whether the time drift corresponds to at least a certain gain; the regulation circuit and the electromechanical device being arranged to be able, when the time drift measured corresponds to said at least a certain gain, to stop momentarily, during the first half-alternation of a given alternation, the oscillation movement of the mechanical resonator in the direction of this alternation, so as to prolong this first half-alternation relative to a nominal duration (T0/4) envisaged for each natural half-alternation; characterised in that the measuring device and the regulation circuit are arranged to further be able to determine whether the time drift corresponds at least a certain loss, and in that the regulation circuit and the measuring device are arranged to further be able, when the mechanical resonator oscillates with an amplitude within a useful operating range and the time drift measured corresponds to said at least a certain loss, to stop the oscillation movement of the mechanical resonator during the second half-alternation of at least a given alternation so as to prematurely put an end to this second half-alternation, relative to said nominal duration, and to start a next alternation at a time occurring before this nominal duration has been attained since the last passage of the mechanical resonator via the neutral position thereof. - a mechanism for indicating a temporal data item, - a mechanical resonator suitable for having an oscillation movement along a given oscillation axis about a neutral position corresponding to the minimum potential energy state thereof, - a maintenance device of the mechanical resonator forming with this mechanical resonator a mechanical oscillator arranged to pace the working of said mechanism, each oscillation of the mechanical resonator having two successive alternations (A1, A2) between two extreme positions, on the oscillation axis, which define the oscillation amplitude of the mechanical oscillator from the neutral position, each alternation having a first half-alternation and a second half-alternation occurring respectively before and after the passage of the mechanical resonator via the neutral position, - a device for regulating the mean frequency of the mechanical oscillator, this regulation device comprising an auxiliary oscillator, an electromechanical device suitable for stopping during an alternation at least momentarily the oscillation movement of the mechanical resonator in the direction of this alternation, and a regulation circuit arranged to be able to generate a control signal intended for the electromechanical device to activate same;