Definition of datum

First of all, we should clarify some definitions of benchmark, according to the definitions in the national standards GB / t1182, GB / t4249-1996 and GB / t16671-1996.

Datum element: refers to the element used to determine the direction and position of the measured element, and the actual element used to establish the datum on the part and actually play the role of datum, such as an edge, a surface or a hole.

Datum: it is used to determine the point, line and surface on which the geometric relationship on the production object is based, that is, the datum is the starting point, line and surface.