Timepiece mechanism, characterized in that the mechanism comprises: - a deformable rhombus (ABCD) comprising four coplanar segments pivotally connected in pairs by their vertices, including an input segment adjacent to an output segment, both pivoted about a pivot axis perpendicular to the plane of the rhombus and passing through a first vertex which is common both to the input segment and to the output segment and which is locked in translation in the plane of the rhombus (ABCD), - a lever mounted to pivot about the pivot axis, the lever being kinematically connected in rotation, about the pivot axis, to a second vertex of the rhombus, opposite to the first vertex, - a first locking member capable of moving between a first locking position, in which the lever is locked in rotation about the pivot axis, and a first unlocking position in which the first locking member does not hinder rotation of the lever, - a second locking member capable of moving between a second locking position, in which the second vertex is locked in translation in a radial direction relative to the pivot axis, and a second unlocking position in which the second locking member does not hinder radial movement of the second vertex, the mechanism being arranged such that one of the first locking member and the second locking member is in its locking position when the other of the first locking member and the second locking member is in its unlocking position, - a control device capable of controlling the movement of the first locking member between its first locking position and its first unlocking position, and in that the angular position of the output segment represents an output value that varies in a similar manner to an input value when the first locking member is in its first unlocking position, and varies inversely to said value when the first locking member is in its first locking position, the input value being represented by the angular position of the input segment. - a deformable rhombus (ABCD) comprising four coplanar segments pivotally connected in pairs by their vertices, including an input segment adjacent to an output segment, both pivoted about a pivot axis perpendicular to the plane of the rhombus and passing through a first vertex which is common both to the input segment and to the output segment and which is locked in translation in the plane of the rhombus (ABCD), - a lever mounted to pivot about the pivot axis, the lever being kinematically connected in rotation, about the pivot axis, to a second vertex of the rhombus, opposite to the first vertex, - a first locking member capable of moving between a first locking position, in which the lever is locked in rotation about the pivot axis, and a first unlocking position in which the first locking member does not hinder rotation of the lever, - a second locking member capable of moving between a second locking position, in which the second vertex is locked in translation in a radial direction relative to the pivot axis, and a second unlocking position in which the second locking member does not hinder radial movement of the second vertex, the mechanism being arranged such that one of the first locking member and the second locking member is in its locking position when the other of the first locking member and the second locking member is in its unlocking position, - a control device capable of controlling the movement of the first locking member between its first locking position and its first unlocking position,