Machining plant emphasizes that machining must meet certain precision, which means that the actual geometry parameters of the steel parts after machining are consistent with the idealized values required by the part drawings. The level of inconsistency between them is called production-processing bias. There are three levels of manufacturing precision in a machining plant: On the one hand is the precision of the specifications, which limits the standard deviation between the production and the processing surface to be within the necessary range; on the other hand is the precision of the geometric patterns, limit the appearance deviation of macro-economic geometries, such as roundness, cylindricity, parallelism and straightness. On the other hand is the precision of each other's parts, limit the deviation between the two standard parts, such as coaxiality, flatness and parallelism, etc. . The precision of production processing is that the main parameters of the actual specification, shape and position of the surface layer of the parts are in line with the main parameters of the idealized geometry stipulated in the engineering drawings. The main parameters of an idealized geometric figure are, in the case of a specification, mean size; in the case of a surface geometric figure, circles, cylinders, plans, spheres, and parallel lines; and in the case of the mutual parts between the surfaces, it is said that the parallel plane, vertical, coaxial output, symmetry and so on. The offset of the main parameters of the actual geometry and the idealized geometry of the parts produced by the machining plant is called the production deviation. Production processing precision and production processing deviation is the evaluation of the production process surface geometric parameters of the main terms. The production process precision is considered by tolerance grade, the smaller the grade value, the higher the precision, and the production process deviation is expressed by standard value, the larger the standard value, the greater the deviation.