Timepiece regulating member comprising an index-assembly system provided with locking means

A regulating member for a horological movement comprising:

• a balance, a balance spring, and an index-assembly system for adjusting a rate of the balance spring, the index-assembly system comprising a stud-holder comprising a first portion comprising a first stud and a second portion comprising a second stud, the first portion being movable relative to the second portion to be able to set a rate of the regulating member, wherein the regulating member comprises a locking device configured to block the second portion of the stud-holder in one position with respect to a plate of the movement,
• wherein the balance spring comprises a coiled strip and an adjustment device for adjusting a rigidity of the balance spring fitted with a resilient element arranged in series with the coiled strip, the stud-holder being mechanically linked to the resilient element,
• wherein the adjustment device comprises a prestressing device for applying a variable force or torque on the resilient element, and
• wherein the resilient element and the prestressing device are arranged between the first stud and the second stud, the first stud being movable relative to the second stud to actuate the prestressing device, a movement of the first stud modifying the rigidity of the balance spring.