How many satellites must the receiver compute range from for proper functionality?

For proper functionality and accurate positioning, a GPS receiver must compute its range from at least four satellites. This is because each satellite provides a signal that includes time and positioning data, which allows the receiver to triangulate its exact position in three-dimensional space.

With signals from three satellites, the receiver can calculate a two-dimensional position (latitude and longitude), but it won't be able to determine altitude as precisely. The fourth satellite is needed to resolve the ambiguity in the timing of the signals, which is critical for accurate three-dimensional positioning. Essentially, the fourth satellite helps to correct for any time discrepancies in the receiver's clock, ensuring a precise fix on the user's location.

This principle is essential in maritime operations, where accurate positioning is crucial for navigation and safety at sea.