This GPS receiver was designed for use on board ship. It is contained in a metal alloy case with a keypad and digital readout are at the front and most of the connection sockets at the back, including the connection to an external antenna.

GPS is a satellite-based navigation system. A group of satellites circles the earth twice a day in a precise orbit. GPS receivers take the satellite signals and use triangulation to calculate the user’s exact location. To do this, the receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the receiver how far away the satellite is. By comparing the measurements from at least three satellites, the receiver can determine the user’s position. Once the user’s position has been determined, the GPS unit can calculate other information, such as speed and heading.

The GPS satellite network was put into orbit by the U.S. Department of Defense in the 1970s and was originally intended for military applications only. But the U.S. government made it available for civilian use in the 1980s. Since then it has become the main system of navigation for almost all vessels, due not only to its accuracy, but also to the fact that it works in all weather conditions, throughout the world, 24 hours a day. The size of receivers has also dramatically decreased since the first commercial receivers were produced, with hand-held receivers becoming widely available by the 1990s.