GB/T 39482.3-2020 "Electrochemical impedance spectroscopy (EIS) on coated and uncoated metallic specimens — Part 3: Processing and analysis of data from dummy cells" applies to the processing and analysis of EIS data for coated and uncoated metallic specimens, using dummy cells to simulate high-impedance coated specimens. It specifies four equivalent circuit combinations, to be operated within a Faraday cage, with an amplitude of 20 mV and a frequency range of 10⁻²–10⁴ Hz. Data quality is verified by comparison with Bode plots, requiring a phase angle deviation of ≤5° in the low-frequency region. The standard clarifies requirements for curve fitting, data representation, and equipment calibration, thereby enhancing the reliability of test protocols.