A minimum parallax stylus detection subsystem is disclosed for use with a graphic input grid overlay which is positioned on the viewing surface of a display device. The invention has a three phase operation wherein, during the first phase, the stylus is at a remote distance from the viewing surface of...http://www.google.de/patents/US4764885?utm_source=gb-gplus-sharePatent US4764885 - Minimum parallax stylus detection subsystem for a display device
