The van der Pauw Method is a technique commonly used to measure the resistivity and the Hall coefficient of a sample. Its power lies in its ability to accurately measure the properties of a sample of any arbitrary shape, as long as the sample is approximately two-dimensional (i.e. it is much thinner than it is wide), solid (no holes), and the electrodes are placed on its perimeter . The van der Pauw method employs a four-point probe placed around the perimeter of the sample, in contrast to the linear four point probe : this allows the van der Pauw method to provide an average resistivity of the sample, whereas a linear array provides the resistivity in the sensing direction.  This difference becomes important for anisotropic materials, which can be properly measured using the Montgomery Method , an extension of the van der Pauw Method .