Hardness is a measure of how mechanically resistant a material is to the mechanical restistance of a harder body (indenter).
On e of the hardest natural material is diamond. That will be used as an indenter especially industrial.

- more info for Rockwell and Brinell
 

It is one of the standardised methods (ISO 6506, ASTM E10).

The Brinell method has a test load range of 1 to 3000 kgf, which means 

it is an optical method.
The main indenters are 2,5 mm, 5 mm and 10 mm ballholders.

Main loads are HBW2,5/187,5 , HBW5/750 and HBW10/3000

Hardness testing is one of the most frequently employed methods for mechanical material testing, in particular for metals.

It provides a simple method for quality control.

For special hardness testing machines, the methods for Rockwell and Brinell will be mainly used!

It is one of the standardised procedures (ISO 6508, ASTM E18).

The process is used to test hardness in the macro range (test force = 150 kgf

It is a differential-depth method. This means that the residual depth of indentation left by the indenter is measured to determine the hardness value.