The art of probe development consists of realizing a probe construction that can apply the required magnetic field (and with that the eddy current field) at the necessary excitation frequency with optimum alignment and the required strength to the location to be tested in the workpiece, but always minimizes unwanted effects as much as possible. Basically the best test instrument can only gather the information that the sensor technology can acquire in the first place. A “blind” probe cannot facilitate sensitive testing. Another decisive factor in addition to this basic sensitivity is the exact reproducibility of the probes.