The principle of HUD (Head-Up Display) isakin to slide projection. Light information is emitted by a projector,reflected by a "reflector" onto a "projection lens", andthen reflected onto the windshield by the "projection lens". Thehuman eye perceives a virtual image located 2-2.5 meters away from the driver.The position of the HUD image on the windshield is adjustable. By changing theangle of the "projection lens", the position of the HUD image projectioncan be adjusted.