It takes four GPS satellites to calculate a precise location on the Earth using the Global Positioning System: three to determine a position on the Earth, and one to adjust for the error in the receiver's clock. If you were 15,000 miles from only one satellite (satellite with red sphere), you could be anywhere on an imaginary red sphere that has a radius equal to the number of miles from the satellite (15,000 miles). Click on the arrow below to see what happens when you add another satellite.

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GPS satellites and positioning - one satelite


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