Abstract: An apparatus, and the method of using it, comprising one, or more, electronic sensors attached to a part(s) of a human or animal's body. The patient then performs an activity, or has an activity performed on them, and the results of the measured parameters are recorded by the sensor and processed, or downloaded and processed. The sensor may include a range of instrumentation, e.g. accelerometers, magnetometers, gyroscopes, force sensors, etc. to record positions (in the X, Y and Z planes), movements, angular movements, forces, stresses in bones/joints, etc. The use of the apparatus and method are appropriate to medical treatments, and perfecting sporting or dancing techniques and the results are processed to give the clinician or coach appropriate information to improve the problem being addressed. Methods for measuring lateral angular movement of hinged joints and spinal extension are taught.