Timepiece mechanism with adjustable inertia balance wheel

A timepiece balance wheel with adjustable inertia, comprising:

• a staff carrying a rim via at least one arm and an inner flange fixed to said staff and directly or indirectly carrying an outer ring with, between said inner flange and said outer ring, a plurality of first elastic guide connections, which are inertia balanced with respect to an axis of said staff and in a plane perpendicular to said axis, said outer ring being distinct from said rim and configured to pivot with respect to said inner flange under the action of an external torque exerted against a resistant torque exerted by said first elastic guide connections, said balance wheel including a plurality of inertia blocks each carried by said outer ring by means of at least one external flexible strip, wherein each said external flexible strip is capable of being indexed in a stable angular position defined by the cooperation between a first indexing toothing carried by said inner flange and a second indexing toothing which is carried by each of said inertia blocks, and in that any rotation of said outer ring with respect to said inner flange modifies an angular position of said inertia blocks, said outer ring including guide shoulders sliding on centring supports comprised in said inner flange.