Oscillating weight for an
automatic watch, arranged to carry a bearing defining an axis of rotation (A-A) and intended to be mounted on the frame of the watch, including a
mass member having a centre of gravity (G) shifted with respect to the axis of rotation. In this weight, this
mass member includes: two parts that can be moved one (10, 18) in relation to the other (24), and arranged such that their relative movement causes a radial movement of the centre of gravity (G) of the
mass member, and a securing device (13, 14, 16b) cooperating with the first and second parts, capable of occupying a first state in which said parts can be moved with reference to each other, and a second state in which said parts are rigidly secured to each other.