For shore-based optical landing systems, the lights are typically mounted on a mobile unit that plugs into a power source. Once set up and calibrated, there are no moving parts to the unit. Shipboard units are much more complicated as they must be gyroscopically stabilised to compensate for ship movement. Additionally, shipboard units are mechanically moved (the "roll angle") to adjust the touchdown point of each aircraft. With this adjustment, the tailhook touchdown point can be precisely targeted based on the tailhook-to-pilot's-eye distance for each aircraft type.
