DGPS machine
The Global Positioning System (DGPS) is a satellite-based navigation system made up of a network of 24 satellites. DGPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. DGPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the DGPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the DGPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.