A method and system for computing the phase shift or the amplitude of an electromagnetic three-phase system. The method comprises the following steps of: detecting vector values corresponding to an electromagnetic quantity by three sensors, the three sensors delivering signals that are offset from each other substantially by 0°, 120° and 240°; computing changed vector values by logically adjusting one of the detected vector values to a phase of 0°; and iteratively computing the phase shift of the three-phase system using the changed vector values.