Test block calibration

Calibration means: align the hardness tester with reference plates so that the measured values are correct. Do this regularly, otherwise you'll measure garbage and the parts will end up either too soft or too hard – and that causes cracks or breakage. Take the plates, check the machine, and compare the values with the manufacturer's standards. If something doesn't match, investigate and recalibrate. Write down the values, then you'll immediately see if the machine is slowly drifting.