The method for measuring the thickness of nonconductive coatings on nonmagnetic base metals using an eddy current thickness gauge is specified in GB/T 4957-2003. This standard applies to the thickness measurement of most anodic oxide coatings, but not all conversion films, especially those with too thin thickness. The standard recommends the use of the magnetic method in GB/T 4956 for measurement in applications on magnetic base metals. The eddy current thickness gauge generates eddy current on the surface of the sample by generating a high-frequency electromagnetic field. The amplitude and phase of the eddy current are related to the thickness of the nonconductive coating. Measuring accuracy is affected by the thickness of the coating, the electrical performance of the base metal, the thickness of the base metal, the edge effect, curvature, surface roughness, foreign attachments, probe pressure, probe placement and sample deformation. Measurement accuracy should be calibrated before measurement to ensure that the standard requirements are met.