What does clock bias refer to in GPS measurements?

Clock bias in GPS measurements specifically refers to the discrepancy between a GPS receiver's clock and standard time. In GPS technology, each satellite has an onboard atomic clock that provides precise time signals to the GPS receivers on the ground. However, these receivers often rely on less accurate quartz clocks, which can drift and lead to timing inaccuracies.

The presence of clock bias affects the calculated distances from the satellites, as the time it takes for signals to travel from the satellite to the receiver is dictated by these clocks. If the receiver's clock is not perfectly synchronized with the atomic clocks of the satellites, it creates a bias that can lead to errors in the calculated position, as the calculated distance will not reflect the true distance due to timing discrepancies.

In contrast, the other options focus on different aspects of GPS measurements but do not accurately define clock bias. While measurement equipment can wear over time, this is distinct from the concept of clock bias itself, which is primarily concerned with timing discrepancies. The differences in time zones pertain to regional standard times rather than the technical alignment of clocks. Lastly, delays in satellite signal transmission are related to communication aspects but do not capture the essence of clock bias, which specifically involves the synchronization of timekeeping devices.