Scratch, rebound and indentation hardness testing methods are the three main ways to determine how resistant metals are to outside forces that may permanently alter their shapes. Testing processes such as the Knoop, Vickers or Rockwell Hardness test utilize the same basic physical principles to produce quantifiable information and values.
Within each of the three main types of measurement, there are individual measurement scales. Some tables allow results to be converted from one scale or testing method to another. Testing the hardness of a metal can provide valuable information regarding its elasticity, yield strength and ability to withstand compression forces without fracturing.