We use g as a hardness unit. It is deceleration, 1 g = 9,81 m/s2. The hammer has a certain speed
before collision and it stops when it hits to the surface of the roll. The harder the roll is, the faster
the movement of the hammer stops, the higher the deceleration of the hammer in the collision is,
so high g = high hardness. MEAN g is the average hardness of the measured profile. SD g is the
standard deviation of the measured hardness profile and COV % is the SDg devided by MEANg.