In magnetotellurics or in electrical prospecting using a uniform primary field, it is necessary to study the effect of the distance between the two electrodes on the measurements of the electric field. For archaeological prospecting, this is even more important due to the small volume of the searched or target features. A series of experiments on the artificial wall of the Centre de Recherches Géophysiques establishes that the electrical sensor one meter apart has a quasipunctual response. It describes very precisely field variations as given by theoretical calculations. Then it can be used without restriction in archaeological prospecting.