Head-up display ( Head up display ), hereinafter referred to as HUD, is widely used in aircraft flight auxiliary apparatus. As the mean pilots do not need to be able to see him down important information. HUD appears the earliest in aircraft, reduce pilot looked down meter frequency, avoid attention disruption and loss on state of consciousness ( Situation Awareness ) master. Because the HUD convenience and can improve the flight safety, aviation machine also in succession follow-up installation. Part of the car industry is also similar to the device as a means of marketing to attract customers, but are not widely used.