The fluxgate gradiometer FM-256 of Geoscan Research is used to measure the slight variations of the intensity and vertical component of the magnetic fields in the subsoil placed under its sensors.

Given that certain archaeological features and, overall, iron objects, combustions (hearths, kilns), earthworks, ditches, silos, pits and graves, produce an alteration in the natural magnetism of the soil were they are placed, they can be detected and measured by this surveying technique. It is the faster one, allowing us to survey 3.800m² per day with a single sensor.