Watch comprising a movement, with a balance comprising a ring distinct from the balance rim, elastically fixed to a flange with respect to which this ring is movable in rotation to modify the position of inertia blocks elastically carried by the flange, each able to be indexed in different stable angular positions corresponding to a different inertia of the balance, the movement including an operating member movable between coupled and uncoupled positions which includes a stop means for immobilising the rim in a coupled position, and a control means for rotating the ring to modify the position of the inertia blocks in the coupled position, the watch including a crown controlling the control means, a rotating coupling ring controlling the coupling/uncoupling of the operating member through contactless interaction with an external adjustment tool.