QJ 990.3A-2011 "Coating inspection methods, Part 3: Coating thickness measurement" specifies the general requirements, methods, detection quantity and location, measurement uncertainty and reporting method for the measurement of Coating thickness on metal substrates using magnetic thickness gauges and eddy current thickness gauges. This standard applies to the measurement and acceptance of Coating thickness such as aerospace products, including organic coating coating, thermal spraying, enamel, etc. But it does not apply to Non-metallic substrates, metal substrates with small radius of curvature, etc. The standard refers to relevant standards such as GB/T 6462, GB/T 12334-2001 and JJF 1059-1999 to ensure the accuracy and Reliability of measurement results.