A microscope calibrator probe includes a handle, a tool head connected to the handle, a viewable target connected to an end of the tool head opposite the handle, and three or more position signaling devices disposed on the handle for tracking the probe in an image guided surgery system. The tool head...http://www.google.co.uk/patents/US5999837?utm_source=gb-gplus-sharePatent US5999837 - Localizing and orienting probe for view devices
