This International Standard specifies a procedure for the verification of dry-film thickness against nominal dry-film thickness on rough surfaces, including the adjustment of the instruments used, the definition of inspection areas, sampling plans, measurement methods and acceptance/rejection criteria. For the purposes of this standard, any specified thickness is taken to be nominal as defined in ISO 12944-5, and the dry-film thickness is the typical thickness above the peaks of the surface profile. The procedure described in this International Standard is based on the use of instruments of the permanent magnet, electromagnet and eddy current type. Instrument accuracy is verified both at zero and at a known thickness on a smooth surface and adjusted if necessary. Measurements taken on a coating on a roughened steel substrate will therefore be higher than the actual value above the peaks of the profile. The thickness of the dry film above the peaks of the profile is defined as the instrument reading minus an appropriate correction value. The dry-film thickness is obtained by using the appropriate correction value applied to readings based on adjustment on a smooth, flat steel surface. Where individual readings, based on adjustment on a smooth, flat steel surface without the use of correction values, are specified or agreed, it is important to recognize that this method does not conform with this International Standard. This standard is applicable if the nominal dry-film thickness is 40 µm or greater. NOTE If the nominal thickness is less than the surface roughness of the substrate, the uncertainty of the measurement will increase.