Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Indentation hardness measures the resistance of a sample to material deformation due to a constant compression load from a sharp object; they are primarily used in engineering and metallurgy fields. The tests work on the basic premise of measuring the critical dimensions of an indentation left by a specifically dimensioned and loaded indenter. Common indentation hardness scales are Rockwell, Vickers and Brinell. A small area is sanded smooth to allow for a flat surface for the indenter to leave an impression. The impression is analyzed to reveal the hardness value for the sample.