A head-up display system in a military aircraft provides projection of flight and weapon-aiming information into the pilot's line-of-sight through a partially-transparent reflector. The pilot operates a button firstly when he recognizes a target viewing through the display and then again when he fixes...http://www.google.se/patents/US4034401?utm_source=gb-gplus-sharePatent US4034401 - Observer-identification of a target or other point of interest in a viewing field
