In addition to the official control method (DIN 6868), alternative test methods have been developed in the last few years: the "visuelle Methode" by Eder and the "Stuttgarter Modell." The aim of both methods is mainly to increase practicability and economy. The DIN method, however, demonstrates clear benefits, precision, practicability and economy, and it is the only method that allows a trend analysis at small intervals, which is the basis for possible preventive action.