This part of ISO 16859 specifies methods for direct and indirect verification of test instruments used for determining Leeb hardness in accordance with ISO 16859-1, and also describes when these two types of verification shall be performed.
The direct verification involves checking that individual instrument performance parameters fall within specified limits, whereas the indirect verification utilizes hardness measurements of reference test blocks, calibrated in accordance with ISO 16859-3, to check the overall performance of the instrument. The indirect method may be used on its own for the periodic performance checking in service.
NOTE°1 Direct verification of test instruments included in this standard can only be done where applicable reference values are provided by the instrument manufacturer.
NOTE°2 For testing in directions other than in direction of gravity, the measured hardness number will be biased. For such cases, the correction values shall be provided by the manufacturer.