ISO 4545-1:2017 specifies the Knoop hardness test method for metallic materials for test forces from 0,009 807 N to 19,613 N.
The Knoop hardness test is specified in this document for lengths of indentation diagonals =0,020 mm. Using this method to determine Knoop hardness from smaller indentations is outside the scope of this document as results would suffer from large uncertainties due to the limitations of optical measurement and imperfections in tip geometry. ISO 14577-1 allows the determination of hardness from smaller indentations.
A periodic verification method is specified for routine checking of the testing machine in service by the user.
Special considerations for Knoop testing of metallic coatings can be found in ISO 4516.