The models calculate precise orbital data or ephemeris and SV (space vehicle) clock corrections for each satellite. In other words, monitoring stations make sure everything is working properly. The data obtained is processed at the main control station to determine satellite orbits and update each satellite's message. The master control station uploads ephemeris and clock data to the SVs. The SVs then send subsets of orbital ephemeris data to GPS receivers via radio signals. Antennas on the ground transmit updated information to everyone