At least two pairs of magnets are arranged near one another on supports, the pairs of magnets and the supports form, when an item to be stabilized is in a required angular position, a closed magnetic circuit (except for the air gap), with magnets placed in such a direction that their north and south poles successively alternate with one another along the magnetic circuit, an item, sensitive to the magnetic field, is attached to the fixed part and placed inside the closed magnetic circuit, the sensitive item supplies a logic output state corresponding to the “item to be stabilized in the required angular position” when the detected field is less than a predetermined maximum threshold, and a logic state corresponding to the “item to be stabilized not in the required angular position”, when the detected field is greater than a minimum predetermined threshold.