The invention relates to a method of controlling a polyphase reversible rotating electrical machine, known as an alternator-starter, which is intended for a heat-engine motor vehicle and which can operate either as an electrical generator (alternator mode) or as en electric motor in order, for example, to start the heat engine. The machine comprises a rotor with at least one field winding, a target and sensors that monitor the rotation of the rotor. The inventive method is characterised in that, using linear-type sensors that deliver sinusoidal signals after the magnetic target has been read, the signals delivered by the sensors are summed by allocating a coefficient thereto in order to create out-of-phase signals equal in number to the number of sensors. The invention is further characterised in that, for each out-of-phase signal, the sum of the coefficients is zero.