Benchmark Classification

Design Datum (Design Reference) The datum specified on the part drawing to define the position of any other point, line or surface. Process Datum (Process Reference) Any datum employed during manufacturing or assembly. It is subdivided by purpose into: Assembly Datum The datum used to establish the correct position of a part within a sub-assembly or final product. Measuring Datum The datum against which the size and location of a machined surface are inspected. Locating Datum (Work-holding Datum) The datum used to position the work-piece during machining. In the first operation only un-machined (as-cast/forged) surfaces can be used; such a surface is called a rough locating datum. In all subsequent operations previously machined surfaces are preferred; these are called finish locating datums.