Hardness test with a hand grinder

[frankiee]

I read this from:

http://www.marineengineering.org.uk/Default.htm

under the heading of repair and main engine

"hardness testing of the journal indicated results far in excess of maximums. Spot grinding using a hand grinder to 1.6mm indicated that hardness was still unacceptably high. As this was approaching maximum allowable decision taken to replace crankshaft"

I wish to know how to do a hardness test with hand grinder.