System for detecting the relative movement of body parts having at least two sub- systems (20, 30), i.e. a first sub-system and a second sub-system, wherein the first sub-system is designed for attachment to a first body part, namely the upper jaw or a body area fixedly connected to the upper jaw such as the skull, and the second sub-system is designed for attachment to a second body part, namely the lower jaw, wherein the first body part and the second body part can be moved relative to one another, and wherein the system has a motion sensor system (621, 681, 631, 691) and a calibration sensor system (626, 636), wherein the motion sensor system and the calibration sensor system are different sensor systems wherein the motion sensor system has at least one motion sensor and wherein the calibration sensor system has at least one calibration sensor, wherein the calibration sensor and the motion sensor are part of different sub-systems, wherein - the motion sensor system is designed to detect the relative movement or relative positions of the first body part and the second body part over a movement range, for example by generating data from which the movement trajectory or path of the relative movement of the first body part and the second body part can be obtained or is obtained, and - the calibration sensor system is designed to determine the relative position of the first body part relative to the second body part if - for example only if and/or whenever - the first body part and the second body part are arranged relative to each other in a calibration range, wherein the calibration range optionally comprises the occlusion position between the upper and lower jaw and/or a region adjacent to the occlusion position, wherein the first sub-system has a first sub-system carrier, which is designed for attachment to the first body part and/or wherein the second sub-system has a second sub-system carrier, which is designed for attachment to the second body part and wherein the first sub-system carrier and/or the second sub-system carrier is/are designed to function as carriers for at least one component of the calibration sensor system and the motion sensor system. wherein the motion sensor system has at least one motion sensor and wherein the calibration sensor system has at least one calibration sensor, wherein the calibration sensor and the motion sensor are part of different sub-systems, wherein - the motion sensor system is designed to detect the relative movement or relative positions of the first body part and the second body part over a movement range, for example by generating data from which the movement trajectory or path of the relative movement of the first body part and the second body part can be obtained or is obtained, and - the calibration sensor system is designed to determine the relative position of the first body part relative to the second body part if - for example only if and/or whenever - the first body part and the second body part are arranged relative to each other in a calibration range, wherein the calibration range optionally comprises the occlusion position between the upper and lower jaw and/or a region adjacent to the occlusion position, - the motion sensor system is designed to detect the relative movement or relative positions of the first body part and the second body part over a movement range, for example by generating data from which the movement trajectory or path of the relative movement of the first body part and the second body part can be obtained or is obtained, and - the calibration sensor system is designed to determine the relative position of the first body part relative to the second body part if - for example only if and/or whenever - the first body part and the second body part are arranged relative to each other in a calibration range, wherein the calibration range optionally comprises the occlusion position between the upper and lower jaw and/or a region adjacent to the occlusion position, wherein the first sub-system has a first sub-system carrier, which is designed for attachment to the first body part and/or wherein the second sub-system has a second sub-system carrier, which is designed for attachment to the second body part and wherein the first sub-system carrier and/or the second sub-system carrier is/are designed to function as carriers for at least one component of the calibration sensor system and the motion sensor system.