A geosurvey survey technique that measures the electrical resistance of the ground for the location of buried features and structures. Any electrical exploration method in which current is introduced in the ground by two contact electrodes and potential differences are measured between two or more other electrodes. It relies on the principle that different deposits offer different resistance to the passage of an electric current depending largely on the amount of water present. A damp pit or ditch fill will offer less resistance, stone wall foundations more, than the surrounding soil. It is one of the most commonly used and least expensive geophysical surveying methods. Readings are taken in a grid-pattern of points all over a suspected site. Variation of resistance through a site is caused mainly by differences in the amount of water contained in pore spaces of deposits and structures. The outline of features may be seen if the readings are plotted as a plan. Although the technique is generally known as 'resistivity surveying', most archaeological surveys use only the ground resistance (in ohms). It compares well with magnetic surveying, as the instruments are simple and cheap and also because modern features such as power cables, iron scrap, and standing buildings do not affect the readings.