 Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provides additional vehicle information to be integrated in the calculation process.Satellite-based augmentation systems (SBAS) support wide-area or regional augmentation through the use of additional satellite-broadcast messages.Using measurements from the ground stations, correction messages are created and sent to one or more satellites for broadcast to end users as differential signal.