The ASGSI projects a beam of light, with coloured sectors, from the aft face of the ship. This beam is stabilised to remove the effects of the ship's roll and pitch and provides the helicopter pilot with visual information relating to their approach angle. The coloured sector of the beam seen by the pilot will indicate to them if their approach is above, below or on the correct glide path. The ASGSI is compliant for use with Night Vision Devices (NVD) as defined in STANAG 1445 & DEFSTAN 02-587 part 3. There are various beam configurations available to suit different naval requirements, all of which may be designed to also comply with NVDs.