A. Deviation: In the production process, because the actual size is difficult to meet the nominal size requirements, that is, it is often larger or smaller than the nominal size, the standard stipulates that there is a difference between the actual size and the nominal size. Positive deviations are called positive deviations, and negative deviations are called negative deviations.
B. Tolerance: The sum of the absolute values of the positive and negative deviation values specified in the standard is called tolerance, also called "tolerance zone". The deviation is directional, that is, it is expressed as "positive" or "negative"; the tolerance is not directional, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".
