This standard specifies methods for evaluating roundness error values using the two-point method and the three-point method. It is applicable to the measurement of roundness errors of internal and external circular elements of parts. The standard refines the measurement process of the two-point method and the three-point method and provides correction coefficients to correct the difference between the actual roundness error value and the Measured value. The concepts of measurement plane and direction in the standard help to accurately evaluate roundness errors and ensure the Reliability of test results. This standard is a specific supplement to GB/T 1958 and aims to standardize the measurement and evaluation methods of roundness errors.