The machining factory emphasizes that machining must meet a certain degree of precision, which means that the main parameters of the actual geometric figures of the steel parts after machining are consistent with the idealized values required by the part drawings. And the inconsistent level among them is called production processing deviation.

The production and processing precision of the machining factory includes three levels: on the one hand, the specification precision, which limits the specification deviation between the standard standards between the production and processing surface layers does not exceed the necessary range; on the other hand, the geometric shape precision limits the production and processing. Appearance deviations of macroeconomic geometric figures on the surface, such as roundness, cylindricity, parallelism, and straightness.

On the other hand, it is the precision of the mutual parts, which limits the deviation of the mutual parts between the standards of the two surfaces produced and processed by the machining factory, such as coaxiality, flatness and parallelism. The precision of production and processing refers to the conformity of the main parameters of the actual specifications, appearance and parts of the surface of the parts after production and processing with the main parameters of the idealized geometric figures specified in the engineering drawings.

The main parameters of idealized geometric figures, in terms of specifications, are mean specifications; in terms of surface geometry, they are circles, cylinders, planes, spheres, and parallel lines; for the mutual parts in the middle of the surface , which means parallel plane, vertical, coaxial output, symmetry, etc.

The offset value of the main parameters of the actual geometric figure and the main parameters of the idealized geometric figure is called the production and processing deviation of the parts produced by the machining plant. Production and processing precision and production and processing deviation are all professional terms for evaluating the main parameters of production and processing surface geometry. The production and processing precision is considered by the tolerance grade. The smaller the grade value, the higher the precision; the production and processing deviation is expressed by the standard value. The larger the standard value, the greater the deviation.