For measuring the tread depth of the tyre of a motor vehicle by means of a measuring head containing a laser (67), the laser measuring head is positioned relative to the tyre of the motor vehicle in such a way, that a reference surface or plane adopts a well-defined position with respect to the tyre....http://www.google.ca/patents/US5895845?utm_source=gb-gplus-sharePatent US5895845 - Method and gauge for measuring the tread depth of a motor vehicle tire
