A method for recording the magnitude and phase of the electrical voltage in an electrical three-phase supply network for a fundamental and at least one harmonic is provided. The method includes measuring an electrical three-phase voltage of the supply network, transforming the measured voltage values into polar coordinates using a rotating voltage phasor for the fundamental as a measured reference phasor, and respectively observing values of at least one voltage phasor for the fundamental and of at least one voltage phasor for at least one harmonic to be recorded with the aid of a state observer, and tracking the observed values on the basis of the measured reference phasor.