All of these pyranometers measure the amount of solar short-wave radiation incident on a surface. Because of their accuracy and performance level, the CMP11-L and CMP21-L are classified by the International Organization for Standardization (ISO) and World Meteorological Organization (WMO) as Secondary Standard sensors, representing the highest level of measurements made by pyranometers. In comparison, the CMP6-L is classified as a First Class sensor, which is the middle classification for pyranometers. (Second Class is the lowest pyranometer classification.)