For indirect verification, the accuracy of the testing machine is determined using a series of measurements on calibrated test blocks. The number of test blocks required, the test points to be set, and the requirement of whether the reference indentation of the test block must also be evaluated are all regulated differently based on the standard and the testing method (see graph).
In order for the test to be successful, the repeatability and the deviation of the measurements must lie within limits defined in the standards.
Depending on the standard, indirect verification must be performed every 12 (per ISO) or every 18 months (per ASTM) and after every direct verification (see graph).
