1. Source-to-detector distance in refraction work; offset. 2. The distance to a positioning station, especially when measured directly. 3. The extreme distance at which useful signals can be detected. 4. The row of townships between successive meridian lines six miles apart; R2W indicates a township in the second column west of a reference meridian. See Figure T-11. 5. One of two measurements necessary to determine a location by radar; see drift. 6. In geostatistics, the distance at which a variogram (q.v.) reaches a sill, beyond which there is no correlation. See Figure V-1.