An insulated cable a few hundred meters to several kilometers long is laid parallel to the geological strike direction.
The cable is either grounded at both ends or laid out in a large loop, and energized at low frequencies (less than 1 kHz).
Two receiving coils are moved on lines outside of and perpendicular to the long side of the loop or grounded cable and two components of the resultant field are measured.
Observed field strength ratio readings are used to calculate reduced ratios using a formula determined by the loop size and shape or the grounded wire length and the position of the receiving coils relative to the loop or grounded wire.
It is claimed to have detected large flat lying conductors to a depth of 400 metres.