Signal processing apparatus (1) for measuring hand joint movement comprising a plurality of markers (5) located at particular positions on a hand (20) and further comprising monitoring apparatus (10) to monitor movement of the markers to obtain dynamic positional information of the markers, and the apparatus further comprising a processor (12) to process the positional information to determine hand joint movement, wherein the processor configured to use the positional information of the markers to determine planes associated with respective groups of markers, wherein the processor configured to determine a first plane and a second plane, said planes adjacent to a hand joint, the first plane is substantially determined by a respective group of markers, and the processor configured to determine the second plane by reference to the first plane and the processor further configured to determine a change in angle between the two planes as a result of hand joint movement.
