A tool consisting of metal probes which have an electric current passed between them while they are inserted into the soil.

This instrument is used to measure the variable resistivity of soils; that is, the amount of resistance to the flow of electricity within it.

A soil’s resistivity is a product of the amount of moisture in the soil and its distribution. It varies considerably, and these variations can reflect the presence of buried archaeological features.

Ditches and pits, for example, hold a greater amount of moisture than the surrounding natural soil, and so they are less resistant; whereas, solid features like walls are more resistant.