Bistable hammer for a chronograph mechanism

A chronograph mechanism including:

• (a) an elapsed time indicator member having heart-pieces connected thereto;
• (b) a reset control member;
• and
• (c) a reset device for said indicator member including a hammer having stop members,
• wherein the reset device is mounted in translation between an inactive position, wherein the hammer is disposed away from the heart-pieces, and an active position, wherein the hammer is disposed so that the stop members exert a reset force against the heart-pieces,
• wherein the hammer includes first and second studs, wherein the first and second studs, respectively, are slidably mounted in first and second holes arranged in a part located above the chronograph mechanism, so that movement vectors of the first and second studs between the inactive and active positions are collinear, but not coincident, thereby moving the hammer,
• wherein the first stud is secured to a hammer lever for moving the hammer from the active position to the inactive position,
• wherein the hammer lever cooperates with a bistable type jumper spring that makes each of the two positions of the hammer stable, and
• wherein the hammer lever includes a pin that comes into contact with a different surface of two surfaces of the jumper spring for each position of the hammer, in order to makes the each of the two positions of the hammer stable via the jumper spring.