A position processor can be mounted on the head of an athlete by means of, for example, a head band. The position processor includes a sensor in the form of a twelve position mercury switch for sensing the direction and angle of tilt of the head. The ON/OFF states of the switches of the sensor are sampled...http://www.google.fr/patents/US5300921?utm_source=gb-gplus-shareBrevet US5300921 - Athletic training system
