Abstract: A phase angle error calculation apparatus (100) comprising a light source (102) that emits light according to an indirect time of flight (iToF) measurement technique. A photonic mixer cell (104) generates and stores a plurality of electrical output signals corresponding to a plurality of predetermined phase offset values. A signal processing circuit processes the electrical output signals according to the iToF measurement technique in order to calculate a reference vector and a reference phase angle therefrom. The output signals correspond to measurement at a first level of precision. The circuit processes a subset of output signals according to the iToF measurement technique and calculates a measurement vector and a measurement phase angle therefrom. The subset of the output signals corresponds to measurement at a second level of precision lower than the first level of precision. The circuit calculates a phase angle correction value using the reference phase angle and the measurement phase angle.