Hardness is the resistance of a material to indentation. Hardness is measured by the permanent depth of an indentation that has occurred. Less of an indentation indicates a greater level of hardness. There are three different types of hardness including: indentation, rebound, and scratch hardness. These correspond to three ways of measuring hardness using individualized hardness scales. The Mohs scale is a hardness scale that tests how much deformation occurs when a sharp object is rubbed on a material. This is a test of scratch hardness. The Rockwell, Shore, and Vickers hardness scales are examples of ways to measure indentation hardness. This is done by measuring the dimensions of an indentation caused by a specified tool. Rebound hardness is measured by the Leed and Bennett tests. These hardness scales look at the bounce that occurs when a diamond-tipped hammer is dropped on a surface.