You use test blocks to verify the calibration of the tester, and not your part. Although it is ideal to use a block that’s as close as possible to your part’s hardness, it isn’t that critical. That being said, blocks are selected from different heat treat lots to get the best possible match. Different indenter and force combinations can likewise affect the result of your received block value.

It is recommended that you consider the suggested hardness levels listed in ISO and ASTM documents.