Rockwell hardness (HR) when the sample tested is too small or Brinell hardness (HB) is greater than 450, measured on the Rockwell Hardness,the test methods is to use an angle of 120 degrees or a diamond cone having a diameter of 1.59 mm/3.18mm of the ball, pressed into a certain load at the surface of the test material, determined by the depth of the indentation hardness of the material. Depending on the experimental material hardness can be divided into three different scales to indicate: 

HRA, HRB, the HRC of Rockwell hardness of A,B,C for the three different standards. Called scale A, scale B, scale C. Rockwell hardness test is now a common indentation hardness of all types used in the experiment. Three initial pressure gauge are 98.07N (10Kgf), the last calculated value based on the hardness of the indentation depth. A ruler is used in the cone diamond indenter ball and then pressurized to 588.4N (60Kgf); ruler B using a diameter of 1.588mm (1/16 inch) steel ball as the indenter, and then pressurized to 980.7N ( 100Kgf), so the scale B softer material suitable for testing. Ruler C applies to harder material testing.

HRA is the use of 60Kg load and pressed into a diamond cone is evaluated hardness, high hardness materials used. For example: Carbide. 
HRB is the use of load and 100Kg 1.58mm diameter hardened steel balls hardness obtained for the lower hardness. For example: mild steel, nonferrous metals, annealed steel, cast iron, etc. 
HRC is the use of 150Kg payload and diamond cone pressed into the device to obtain hardness, high hardness materials used. For example: hardened steel.

Superficial Rockwell hardness testing uses three test force, two pressure head, they have 6 combinations, corresponding to the six surface Rockwell hardness scale. Superficial Rockwell hardness test is a complement to the Rockwell hardness test, when using Rockwell hardness test, when faced with a thinner material, the smaller the sample, the test surface hardened layer shallow or surface plating layer on should use surface Rockwell hardness test. Then using the same test with a Rockwell hardness indenter, Rockwell hardness test using only a fraction of the size of the test force, it can be effectively hardness test results on the sample. Superficial Rockwell hardness scale applicable to similar N Rockwell hardness of HRC, HRA and HRD test materials; T scale applicable to similar Rockwell hardness of HRB, HRF and HRG materials testing.