An instrument used in electromagnetic surveying, mainly for the detection of metals, though on a limited scale it can be used to locate archaeological features. The instrument has a transmitter coil, which sends pulses of magnetic field to the ground: the continuous rising and falling of the field produces eddy currents in metal objects, and magnetic fields in susceptible soil. These are detected by a receiver coil. Only shallow features can be satisfactorily located, and it can be used to find metals, graves, and pottery.