What are the reasons for the variation in Rockwell hardness tester readings?

Taiwan Nakazawa introduces for you, regarding the loading mechanism section:
(1) Check whether the testing table is firmly installed on the screw, whether the screw is loose, and whether the testing table is level.
(2) Poor clamping of the indenter or damage to the tip of the indenter.
(3) If the sliding poise on the loading lever is loose, it will cause the test force to be unstable; the sliding poise should be tightened.
(4) Check whether the knives and knife seats on the loading lever are loose; if they are loose, the knives and knife seats should be tightened.
(5) The shoulder plane of the upper part of the spindle and the working surface of the knife seat fixed on the frame are not smooth and flat, causing instability of the test force; the working surfaces should be adjusted or ground.
(6) If the edges of the three knives on the loading lever are not on the same plane or are not parallel to each other, the lever ratio will fluctuate frequently, easily causing instability of the test force. In this case, the knives should be ground or adjusted so that their edges are on the same plane and parallel to each other.