To measure the time taken by the wave to reach it, the GPS receiver compares the transmission time (included in the signal) and reception time of the wave transmitted by the satellite. If the receiver has a clock that is perfectly synchronized with that of the satellites, three satellites are enough to determine the position in three dimensions by triangulation. However, if this is not the case, it takes four satellites to be able to resolve the clock issue and receive the data correctly. A GPS can operate anywhere, just as long as it has an unobstructed view of the sky, 24 hours a day, 7 days a week. However, it’s important to be aware that the position data may be incorrect in the presence of electromagnetic interference.