ÖNORM EN ISO 25178-6 describes a classification system for methods used primarily for the measurement of surface texture. It defines three classes of methods, illustrates the relationships between the classes, and briefly describes specific methods. This classification system provides a context for the development of other parts of ISO 25178 describing characteristics and calibration and measurement standards for some of the individual methods. Such a classification is also intended to aid in choosing and understanding various types of methods and in determining which standards apply to their application. The classification system is aimed to be as general as possible. However, instruments may exist that do not clearly fit within any single method class.