System for measuring rotational imbalances for a balancing machine of a rotating workpiece, - said workpiece defining a rotation and a force determined by imbalances in at least one plane during said rotation, and - said system comprising: - a fixed support - a movable support connected to said fixed support, configured to allow housing at least part of said workpiece and configured to allow micro-movements relative to said fixed support along said plane proportional to said force, - sensing means operatively connected to said fixed support and said movable support and capable of sensing said force, - blocking means constrained in a compliant way said movable support and said fixed support in such a way as to allow said relative micro-movement between said movable support and said fixed support exclusively along a predetermined trajectory lying on said plane, along said predetermined trajectory and including opposing means realizing a moment opposite to the moment generated by said workpiece when positioned on said movable support, - and being characterised in that said blocking means comprise at least one screw developed along said predetermined trajectory, integral with said fixed support and comprising a stem constrained to said fixed support and a head and a guide defined on said movable support, housing said head and defining a perforated bottom suitable to allow the passage of said stem along said predetermined trajectory and to obstruct the movement of said head beyond said bottom; said means of opposition being arranged between said head and said bottom. - said workpiece defining a rotation and a force determined by imbalances in at least one plane during said rotation, and - said system comprising: - a fixed support - a movable support connected to said fixed support, configured to allow housing at least part of said workpiece and configured to allow micro-movements relative to said fixed support along said plane proportional to said force, - sensing means operatively connected to said fixed support and said movable support and capable of sensing said force, - blocking means constrained in a compliant way said movable support and said fixed support in such a way as to allow said relative micro-movement between said movable support and said fixed support exclusively along a predetermined trajectory lying on said plane, along said predetermined trajectory and including opposing means realizing a moment opposite to the moment generated by said workpiece when positioned on said movable support, - and being characterised in that said blocking means comprise at least one screw developed along said predetermined trajectory, integral with said fixed support and comprising a stem constrained to said fixed support and a head and a guide defined on said movable support, housing said head and defining a perforated bottom suitable to allow the passage of said stem along said predetermined trajectory and to obstruct the movement of said head beyond said bottom; said means of opposition being arranged between said head and said bottom. - a fixed support - a movable support connected to said fixed support, configured to allow housing at least part of said workpiece and configured to allow micro-movements relative to said fixed support along said plane proportional to said force, - sensing means operatively connected to said fixed support and said movable support and capable of sensing said force, - blocking means constrained in a compliant way said movable support and said fixed support in such a way as to allow said relative micro-movement between said movable support and said fixed support exclusively along a predetermined trajectory lying on said plane, along said predetermined trajectory and including opposing means realizing a moment opposite to the moment generated by said workpiece when positioned on said movable support, - and being characterised in that said blocking means comprise at least one screw developed along said predetermined trajectory, integral with said fixed support and comprising a stem constrained to said fixed support and a head and a guide defined on said movable support, housing said head and defining a perforated bottom suitable to allow the passage of said stem along said predetermined trajectory and to obstruct the movement of said head beyond said bottom; said means of opposition being arranged between said head and said bottom.