Originally developed in 1973 by the U.S. Department of Defense for military purposes, the Navstar GPS network consists of 24 satellites orbiting the earth every 12 hours and five ground stations that monitor the satellites' position in space and operational status.

In order to accurately determine your location and other data, such as current and average speed, directional heading, and elevation, GPS devices use a receiver to acquire signals from at least four of these satellites. This is known as a 3D fix, and it's why GPS antennas require an unobstructed view of the sky to work correctly.

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