GB1764-79 specifies two methods: the micrometer method and the magnetic Thickness Gauge method. The former is more practical in the case of destructive testing, while the latter has more problems:
First, what if the substrate is not an iron plate?
Second, there is no regulation on what instrument to use,
Third, even if the sample substrate is iron, when the coating contains certain pigments (such as iron red, etc.), the magnetic Thickness Gauge method will not work. In such cases the scope of application of the law must be specified.
