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The validity period for the calibration of a given hardness reference block is specified in part 3 of the ISO standard published for the respective hardness testing process.

The validity for steel hardness reference blocks should be limited to five years, whereas the validity period can be reduced to two to three years for aluminium and copper alloys.

According to the standard, no subsequent rework may be carried out on the hardness reference blocks.

However, hardness reference blocks do not lose their certified properties on the very day that the calibration certificate expires, recalibration of the respective hardness reference block by an appropriately certified respectively accredited company is possible.