Hardness can be defined as a resistance of material to indentation. All hardness test have one thing in common, a certain form of indentation is used to impress the surface of material.
The difference is the manner in which the hardness is measure. Hardness is not a fundamental property of a material, but a response to a particular test method.
The traditional Rockwell, Brinell or Vickers hardness testing machines require the test piece to be brought to the laboratory; however, in cases such as an in-service component, it is not possible. As such, portable hardness testing devices have been developed that permit in-situ hardness measurements thus offering quick and economical supplements to conventional laboratory testing machines. There are two different physical methods recognized in the practical field for many applications namely Vickers- diamond and rebound method. The choice depends on the type of application.