A system determines the position of an elevator car movable in an elevator installation shaft. A transmitter emits modulated electromagnetic radiation with a first modulation frequency as a first output signal, a sensor cell receives electromagnetic radiation reflected by a detected object as an original measurement signal, and an evaluation unit, communicating with the transmitter and the sensor cell, delays the original measurement signal thus generating a delayed measurement signal, determines a first phase offset between the original measurement signal and the first output signal, determines a second phase offset between the delayed measurement signal and the first output signal, selects either the first phase offset or the second phase offset based upon a selection condition to determine a position of the elevator car within a portion of the elevator shaft, and determines the elevator car position based upon the elevator shaft portion and the position within the portion.