Also called a Reference Station. In GPS navigation, this is a receiver that is set up on a known location specifically to collect data for differentially correcting data files of another receiver (which may be referred to as the "mobile" or "rover" receiver). In the case of pseudo-range-based Differential GPS (DGPS) the base station calculates the error for each satellite and, through differential correction, improves the accuracy of GPS positions collected at unknown locations by another (roving) GPS receiver. For GPS Surveying techniques, the receiver data from the base station is combined with the data from the other receiver to form double-differenced observations, from which the baseline vector is determined.