True position tolerance is evaluated relative to which frame?

• A. The datum reference frame.
• B. The material reference frame.
• C. The production frame.
• D. A nominal frame.

Answer: (A)

True position tolerance is evaluated with respect to the datum reference frame because that frame defines the coordinate system anchored by the part’s datums. The datum reference frame establishes the exact reference from which the feature’s true position is measured—the ideal location and orientation defined by the datums. When inspectors check true position, they compare the actual feature location to this ideal position within the DRF, and the tolerance zone is oriented and located based on that same frame. Other frames don’t provide the standardized inspection reference used for true position: the material reference frame follows the part’s material orientation, the production frame isn’t a standard inspection frame, and a nominal frame merely represents perfect geometry, not the actual measurement reference.