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Datum reference frames
The drawing datum scheme and the physical fixture are related descriptions, not interchangeable objects. Datum precedence affects the intended setup.
This reference collection concerns light, offline dimensional-inspection layouts. It brings locating concepts, component descriptions and revision records together without substituting for an engineered fixture design. The drawings are original explanatory diagrams. Reference IDs identify documents, not commercially tested products. Read the scope and limitations alongside each example, and keep the actual part drawing and inspection requirements available when reviewing a proposed layout.
Practical example
Place the drawing reference beside each contact group and mark which face is loaded first.
A convenient flat face is not automatically a specified datum feature.