Assembly for attaching a balance spring for a horological movement, balance spring and method for adjusting the beat and rate of a sprung balance assembly

An assembly (1) for the removable attachment of a balance spring (2) of a horological movement comprising a balance bridge (4), said assembly comprising the balance spring (2) on the one hand, a retaining means (8) for the balance spring (2), and a removable locking part (10) on the other hand, the balance spring (2) comprising a coil winding (12) which extends between a first free end (14) of an inner first coil (16) and a second free end (18) of an outer last coil (20), the second free end (18) of the outer last coil (20) of the balance spring (2) including an attachment means in which the retaining means (8) is engaged in order to ensure the removable attachment of the balance spring (2) by its outer last coil (20), the attachment means being dimensioned so that, in its natural rest position, the attachment means is not in contact with the retaining means (8) engaged in this attachment means, the locking part (10) for removably attaching the second free end (18) of the outer last coil (20) of the balance spring (2) being mounted on the retaining means (8) to lock the attachment means.