A station to which reference can be made, to normalize measurements made at out-stations. Geophysical parameters measured at base stations are presumed to be known very accurately and preferably absolutely. For example, in a gravity survey, the base station is used to determine instrumental drift and to provide an absolute value to which gravity anomalies relate. In magnetic surveying, a continuous-reading magnetometer may be used at a base station to monitor the diurnal fluctuations in the Earth’s geomagnetic field and thus aid the interpretation of magnetic survey data.