The twin electrode is the most useful instrument for testing resistivity. It is a frame containing a meter, batteries (to provide power) and two probes, usually half a metre apart, but this distance can be altered when a deeper survey is required. Two remote probes and a connecting cable are also necessary; this links the probes when placed at least thirty times the distance between the static probes. For example, if the primary or static probes on the frame were one metre apart (in the instance of a deep survey) the remote probes would need to be placed a minimum of thirty meters from the area under investigation. It is this that makes the process more complicated than other methods, such as magnetometry. The most accurate results can be obtained in the summer months, in the case of temperate climates, as the soil moisture content is lower then, so the equipment can detect differences in resistance more easily.

An electrical current is passed through the ground between the two electrodes in order to measure the resistance. It is more difficult for the current to pass through drier, more compact material, such as a buried wall of a house or an ancient road than it would be for it to pass through damp clay soil, which it would penetrate relatively easily.