Which statement best defines a datum reference frame (DRF)?

Which statement best defines a datum reference frame (DRF)?

• A. It is a single datum used as the origin for all measurements.
• B. It is the coordinate system established by the chosen datums to measure features.
• C. It is a measurement method independent of datums.
• D. It is the physical jig used to hold the part during inspection.

Answer: (B)

In GD&T, a datum reference frame is the coordinate system used to locate and measure features. It’s formed by the chosen datums and their orientations, providing an origin and three mutually perpendicular axes (often labeled X, Y, and Z) that define how measurements are made and how tolerances are evaluated. This frame is what tolerance values in a feature control frame are referenced to, so you can assess true position, orientation, and other traits relative to those datums. That’s why the best statement is the one that describes the DRF as the coordinate system established by the chosen datums to measure features. It emphasizes that the frame is a definable system derived from datums, not just a single datum, not a separate measurement method, and not a physical jig. The other ideas misrepresent the DRF by treating it as a single datum, a datums-free measurement method, or a holding fixture, rather than the virtual coordinate system created by the datums for measurement and inspection.

In GD&T, a datum reference frame is the coordinate system used to locate and measure features. It’s formed by the chosen datums and their orientations, providing an origin and three mutually perpendicular axes (often labeled X, Y, and Z) that define how measurements are made and how tolerances are evaluated. This frame is what tolerance values in a feature control frame are referenced to, so you can assess true position, orientation, and other traits relative to those datums.

That’s why the best statement is the one that describes the DRF as the coordinate system established by the chosen datums to measure features. It emphasizes that the frame is a definable system derived from datums, not just a single datum, not a separate measurement method, and not a physical jig. The other ideas misrepresent the DRF by treating it as a single datum, a datums-free measurement method, or a holding fixture, rather than the virtual coordinate system created by the datums for measurement and inspection.