What is a Datum Feature?

A datum feature is fundamentally a feature of a part that serves as a reference point for measurement and configuration in the context of geometric dimensioning and tolerancing. It establishes a framework for the interpretation of other features and helps ensure consistency in manufacturing and inspection processes. When identifying a datum feature, it often designates a specific surface, line, or point from which other measurements are taken, making it crucial for achieving desired tolerances and ensuring that parts will fit together correctly in an assembly.

In the context of the other options, a geometric control pertains to how features are controlled but does not specifically identify the reference feature needed for measurement. A surface used to measure angles is a more specialized function that does not encompass the broader definition of a datum feature. Lastly, a measurement tool pertains to the instruments used in measurement rather than a specific part feature designated as a reference point. Therefore, the correct answer accurately reflects the role of datum features in geometric dimensioning and tolerancing.