Finally, we review a few of experimental works related to crack determination for Laplace's equation. Detecting cracks by using DC or AC currents is actually a common practice in engineering. For example a technique known as the `potential drop method' which detects cracks by scanning a pair of electrodes on the surface of a conducting material belongs to this category. Information about cracks is obtained by giving a fixed amount of DC current to the material to be inspected, and then by measuring the resulting voltage between the electrodes. As a recent work of this type we can mention a paper by Saka et al., where they determined the depth of a 2D surface crack using a calibration curve obtained with FEM. The work by Kubo's group[18,36], mentioned earlier, deals with the determination of interior cracks. They could determine an elliptical crack in a 3D experiment. In addition to these `true NDT' experiments, one can mention a paper by Liepa et al. where these authors tried to see if they can detect a metal plate in a water tank with electrodes on the wall. This experiment is supposed to simulate the crack determination via analogy.