Your hardness reference plate has been carefully calibrated. To ensure that you can accurately reproduce the calibrated hardness value as often as possible, care should be taken when handling the hardness comparison plate.
This already starts with proper storage: always store the hardness comparison plate in its box. Even the slightest scratches or corrosion can influence the test results. Such damage cannot be remedied by grinding and polishing. A plate treated in this way can no longer serve as a reference.
Also make sure that you use a hardness reference plate for the appropriate test procedure. A color and symbolic ordering system on the packaging helps you to avoid confusion.
Keep the work surroundings and hardness bench as clean as possible. The test and support surface of the plate and the machine table must be free of grease and dust. Again, even the smallest particles that are between the probe and hardness reference plate or squeezed on the support, can change the test result.
Of course, you want to use your hardness comparison plate as often as possible. Nevertheless, keep the minimum distances between the test impressions. Due to structural changes in the impression area, this is absolutely necessary. This also applies to the distance to the edge of the plate.
If you adopt this handling of your hardness reference plates, you can efficiently use them for periodic daily inspection of your hardness testers and ensure accurate test results.