A rotary encoder system, comprising: a plurality of tracks (12, 14) fixed to a rotary shaft that is configured to rotate circumferentially about a longitudinal axis of the shaft, each of the plurality of tracks (12, 14) comprising a set of track elements (20, 22) arranged continuously along a circumferential surface of each respective track (12, 14), the track elements of at least one of the sets of track elements (20, 22) are modulated non-uniformly along the track, and the track elements of the at least one of the sets of track elements and the other set of track elements are modulated differently, each of the set of track elements for the at least one modulated track of the plurality of tracks having a circumferential length that varies along the circumferential surface of the at least one modulated track to provide the at least one modulated track with a nonlinear modulation along the at least one modulated track; and for each of the plurality of tracks, the rotary encoder system comprises two sensors (24, 26; 28, 30) positioned adjacent to the corresponding track, a reference sensor (24, 28) located at a reference angular position and a second sensor (26, 30) located at an angular position that is angularly shifted relative to the corresponding reference angular position by a predetermined mechanical angle, each given sensor being configured to provide a respective sensor signal, each of the sensors (24, 26, 28 and 30) being arranged for sensing position or movement of the respective set of track elements (20, 22) and for providing respective sensor signals representing position or movement of the track elements (20, 22), wherein the at least one sensor (28, 30) positioned adjacent to the at least one nonlinearly modulated track is configured to provide a sensor signal that varies according to the circumferential_length of each respective track element of the set of track elements of the at least one modulated track such that the sensor signal completes a period as each of track elements is rotated past the sensor according to the circumferential_length of each respective track element to thereby encode the nonlinear modulation along the respective track, each respective sensor signal being outputted to a calculator, wherein for each of the plurality of tracks, the calculator is configured to compute a reference electrical angle from the signal of the reference sensor (24, 28) and a second electrical angle from the signal of the second sensor (26, 30), and to compute an indication of the absolute rotational position of the rotary shaft based on said reference electrical angles and second electrical angles. a plurality of tracks (12, 14) fixed to a rotary shaft that is configured to rotate circumferentially about a longitudinal axis of the shaft, each of the plurality of tracks (12, 14) comprising a set of track elements (20, 22) arranged continuously along a circumferential surface of each respective track (12, 14), the track elements of at least one of the sets of track elements (20, 22) are modulated non-uniformly along the track, and the track elements of the at least one of the sets of track elements and the other set of track elements are modulated differently, each of the set of track elements for the at least one modulated track of the plurality of tracks having a circumferential length that varies along the circumferential surface of the at least one modulated track to provide the at least one modulated track with a nonlinear modulation along the at least one modulated track; and for each of the plurality of tracks, the rotary encoder system comprises two sensors (24, 26; 28, 30) positioned adjacent to the corresponding track, a reference sensor (24, 28) located at a reference angular position and a second sensor (26, 30) located at an angular position that is angularly shifted relative to the corresponding reference angular position by a predetermined mechanical angle, each given sensor being configured to provide a respective sensor signal, each of the sensors (24, 26, 28 and 30) being arranged for sensing position or movement of the respective set of track elements (20, 22) and for providing respective sensor signals representing position or movement of the track elements (20, 22), wherein the at least one sensor (28, 30) positioned adjacent to the at least one nonlinearly modulated track is configured to provide a sensor signal that varies according to the circumferential_length of each respective track element of the set of track elements of the at least one modulated track such that the sensor signal completes a period as each of track elements is rotated past the sensor according to the circumferential_length of each respective track element to thereby encode the nonlinear modulation along the respective track, each respective sensor signal being outputted to a calculator, wherein for each of the plurality of tracks, the calculator is configured to compute a reference electrical angle from the signal of the reference sensor (24, 28) and a second electrical angle from the signal of the second sensor (26, 30), and to compute an indication of the absolute rotational position of the rotary shaft based on said reference electrical angles and second electrical angles.