Dusting off my engineering lab experiences of 30+ years ago.....
The theory is, you apply a defined weight to a particular testing point (steel ball of a given diameter, diamond, or whatever it is depending on which Rockwell or Brinnell scale you're using) and measure the amount of penetration by the testing point into the piece being tested.
To do this, you put the point on what you're testing and set a slight preload on the point until the tester's dial reads 0. Then trip the lever to apply full test weight. The amount of penetration should read on the tester dial as a hardness number.
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Don't believe everything you know. -- Bumper sticker
Everybody is ignorant, only on different subjects. -- Will Rogers
Law of Logical Argument - Anything is possible if you don't know what you are talking about.