Why does a GPS receiver usually need signals from at least four satellites?

A GPS receiver requires signals from at least four satellites to determine a precise position on Earth.

While a single satellite signal places a receiver somewhere on the surface of an imaginary sphere, processing signals from four satellites allows the receiver's computer to calculate the specific point where all four spheres intersect. This intersection provides the user's longitude, latitude, and altitude.12

Although three satellites could theoretically provide a three-dimensional fix, a fourth satellite is necessary in practice to offset inaccuracies in the receiver's internal clock. Because the receiver must compare its own time to the highly accurate time transmitted by the satellites, any discrepancy in the receiver's clock would lead to significant errors in distance calculations. By using a fourth satellite, the system can resolve this timing offset, ensuring a reliable and accurate location fix.12