Indirect testing according to ISO and ASTM standards

In indirect testing, the accuracy of the testing machine is determined using a series of measurements on calibrated hardness reference blocks. The number of hardness reference blocks required, the test points to be set and the requirement as to whether the reference indentation of the hardness reference block must also be evaluated are regulated differently depending on the standard and test method (see diagram).

For the test to be successful, the repeatability and the deviation of the measurements must be within the limits defined in the standard.

Depending on the standard, the indirect test must be carried out every 12 months (according to ISO) or every 18 months (according to ASTM) and after every direct test (see diagram).