Watch movement with device for setting the frequency of a mechanical resonator

A watch movement comprising:

• a mechanical resonator including a balance, rotatably mounted in a support, and of a spring,
• an escapement comprising an anchor arranged to oscillate synchronously with the balance, and
• a setting device for setting an oscillation frequency of the mechanical resonator,
• the setting device comprising a moving part rotating around a rotational axis of the balance, said moving part comprising fastening means for attaching an outer end part of the spring, and defining means for defining an active length of the spring, that define an end point (EP) of an active part of the spring at a fixed point (FP) on the moving part once the spring has been attached to said moving part by the fastening means, the setting device further comprising variation means for varying the active length of the spring, enabling the oscillation frequency to be set by an angular displacement, relative to said rotational axis and in a chosen direction, of the outer end part relative to the moving part, and thus to said fixed point on said moving part, the setting of the oscillation frequency being combined with a rotation of the moving part over an angular distance substantially corresponding to said angular displacement and in a direction opposite to the chosen direction;
• the watch movement further comprising guide mark means for setting an mechanical resonator guide mark relative to said anchor, wherein the variation means comprise a first toothed wheel, carried by the moving part, and a first toothing, arranged along the outer end part of the spring, with which the first toothed wheel meshes and which can be rotated to perform said angular displacement, said fastening means holding the outer end part by friction so as to enable the first toothed wheel to drive said outer end part via the first toothing and thus to angularly displace the outer end part relative to the moving part and to said defining means, so as to vary the active length of the spring;
• and in that the first toothed wheel is in an intermeshing relationship with a second toothing, integral with the resonator support, such that, when the outer end part undergoes said angular displacement in the chosen direction relative to the moving part, said moving part is simultaneously angularly displaced by said angular distance in the opposite direction.