The "GB/T 30857-2014 Test method for film thickness and film thickness variation of sapphire substrates" standard provides a test method for film thickness and variation of sapphire single crystal substrates (including cut, ground and polished), suitable for gallium nitride thin film epitaxial wafers and sapphire substrates for Miscellaneous applications. The standard describes in detail the specific method for measuring whether the film thickness and film thickness variation of sapphire substrates meet the requirements, and defines related terms such as "5 point Film thickness variation", i.e. the difference between the maximum Film thickness and the minimum Film thickness at a specific 5 point. These test methods ensure quality control of sapphire substrates in production and applications.