If the Rockwell hardness tester shows a large error how should it be maintained and handled?

Taiwan Nakazawa Co., Ltd. suggests for you:
(1) You can remove the worktable and check if its contact surface with the screw is clean.
(2) Check whether the screw protective sleeve is propping up the worktable.
(3) Check whether the indenter is damaged. If the indicator pointer starts to rotate very quickly and then rotates slowly when the main test force is applied, it indicates that there is too little machine oil in the buffer. At this time, you can lift the felt pad at the upper end of the buffer and slowly inject clean machine oil. At the same time, pull and push the handle several times to move the piston up and down repeatedly to completely exhaust the air in the buffer, until oil overflows from the top when the piston sinks to the bottom.