Which statement best describes a datum feature?

Which statement best describes a datum feature?

• A. A datum feature is the target location used for true position measurement.
• B. A datum feature is the theoretical plane used for design.
• C. A datum feature is the measurement reference used to derive the datum.
• D. A datum feature is the actual physical surface used to establish the datum.

Answer: (D)

Datum features are the real surfaces or features on a part that you use to establish the datum reference frame. The datum itself is a theoretical, exact plane, axis, or point created from that surface for measurement, but the feature—the actual physical surface on the part—is what defines where that datum comes from in the real world. That’s why describing a datum feature as the actual physical surface used to establish the datum is the most precise choice. Other ideas mix up roles: a target location relates to where you measure true position, not the surface that defines the datum; a theoretical plane describes the datum itself rather than the physical surface; and a measurement reference used to derive the datum sounds like the datum frame rather than the surface that establishes it. The key is that the datum feature is the tangible surface that anchors the datum.

Datum features are the real surfaces or features on a part that you use to establish the datum reference frame. The datum itself is a theoretical, exact plane, axis, or point created from that surface for measurement, but the feature—the actual physical surface on the part—is what defines where that datum comes from in the real world. That’s why describing a datum feature as the actual physical surface used to establish the datum is the most precise choice.

Other ideas mix up roles: a target location relates to where you measure true position, not the surface that defines the datum; a theoretical plane describes the datum itself rather than the physical surface; and a measurement reference used to derive the datum sounds like the datum frame rather than the surface that establishes it. The key is that the datum feature is the tangible surface that anchors the datum.