Fast and easy layer thickness measurement Measurement of single layer and layer systems Measurement independent of the material Comfortable operation Precise measurement without calibration The ball crater test (Calotest) is a well established method for the determination of layer thickness. With a rotating steel ball and an abrasive slurry, a spherical cap is ground through the coating into the base material of the sample. When examined with a microscope, the layer/base material interface appears as a circle or, in case of a multilayer coating, a system of concentric circles. The layer thickness can be calculated from the diameters of these circles and the diameter of the grinding ball.