The Pferch principle is a compensation method for the evaluation of measured values and one of the basic principles of coordinate measuring technology. Whenever a geometry element is measured with more points than the minimum number of probing points, a scatter indication is obtained. This can make statements about the quality of a measurement and the workpiece. However, probing with more points than mathematically necessary leads to an overdetermination of a standard geometry element. Therefore, a suitable substitute element must subsequently be calculated by a compensation procedure. The Pferch principle is one of these compensation methods, along with the Gaussian compensation method, the enveloping circle principle and the minimum circle compensation method, and calculates a circle such that all measurement points lie outside the circle while the diameter of the circle is as large as possible. For example, geometry data of bores can be determined when checking mating dimensions. Since the pen circle principle, like the envelope principle, is very susceptible to outliers, it is recommended to eliminate them before use.