What assists in communicating how dimensions should be aligned for inspection?

The datum system plays a crucial role in communicating how dimensions should be aligned for inspection. A datum is a reference point, line, or plane on a part that establishes a basis for measurement and serves as the starting point for dimensional control. By defining datums, it becomes clear how other features relate to these reference points, ensuring that inspections can be conducted consistently and accurately.

In GD&T, the datum system provides a framework for controlling the location, orientation, and form of features. This is essential because it helps to eliminate ambiguity regarding how measurements should be taken and how features should be positioned in relation to one another. When inspection personnel have a clearly defined datum system, they can align their measuring tools appropriately, facilitating precise evaluations of the part's geometry.

While dimension lines indicate where measurements should be taken and measurement tolerances specify acceptable variations, they do not provide the same level of reference and alignment direction as a datum system. Reference marks, although useful in some contexts, are not as comprehensive in defining measurement relationships and inspection alignment as a well-structured datum system in GD&T.