When verifying true position, why is a datum frame used?

When verifying true position, why is a datum frame used?

• A. It defines color coding.
• B. It marks the part for painting.
• C. It establishes a reference system for the position of features relative to primary, secondary, and tertiary datums.
• D. It determines the weight.

Answer: (C)

A datum frame provides the reference system used to verify true position by anchoring measurements to the primary, secondary, and tertiary datums. It creates a 3D coordinate frame with a defined origin and orientation, so the true position of each feature is evaluated consistently within that frame. When you check true position, you compare actual feature locations to their theoretical locations inside this datum frame, ensuring measurements are repeatable and tied to the part’s designated datum references, regardless of how the part is mounted or rotated in the inspection setup. Color coding, painting marks, or weight don’t establish or affect positional tolerance, which is why the datum frame is used.