Abstract: Device for detection of relative motions or positions of one or more parts of the body, comprising at least two measuring sensors which are applied to the parts of the body whose motions or positions are to be measured. Signals from the sensors are transmitted to a signal processor for storing and/or analyzing. The measuring sensors are connected to the fulcrums of a parallelogram action linkage which is attached to the parts of the body whose relative movements or positions are to be detected. The imaginary axes about which some of the above-mentioned motions take place form a part of the parallelogram action linkage.