1. A method for detecting and classifying anomalies of a surface of a sample of a material suitable for use as a substrate for storage, display or electronic devices, comprising: supplying radiation to the surface; detecting radiation from the anomalies of the surface and supplied to the surface to provide and output; analyzing the output for anomalies and classifying the anomalies; and varying sensitivity in detecting radiation from the anomalies or a threshold in analyzing the output and using two outputs provided at two or more different sensitivities or two or more different thresholds to arrive at at least one classification of the anomalies.