The Rosiwal scale attempts to give more quantitative values of scratch hardness, unlike the Mohs scale which is a qualitative measurement with relative values.
The hardness is calculated by finding the volume of removed material, but this measurement can be difficult and must sample a large enough number of grain in order to have statistical significance.
[2] Measures the scratch hardness of a mineral expressed on a quantitative scale.
These measurements must be performed in a laboratory, since the surfaces must be flat and smooth.
The base value of the Rosiwal scale is defined as corundum set to 1000 (unitless).