How is the true position interpreted for a feature that sits on two datums A and B?

How is the true position interpreted for a feature that sits on two datums A and B?

• A. The true position must lie within the cylindrical tolerance zone defined by the DRF using datums A and B
• B. The true position is independent of datums
• C. The feature must be equidistant from A and B
• D. The tolerance zone is spherical around the feature

Answer: (A)

True position expresses where the feature’s center or axis must lie relative to the datums. When two datums are used, the datum reference frame defined by those datums fixes both the orientation and the location of that axis. The positional tolerance then becomes a cylindrical tolerance zone whose axis aligns with the feature’s true axis and is located by the DRF established from datums A and B. The actual axis must fall inside this cylinder, enforcing the required position in relation to both datums. This is why the correct description is that the true position must lie within a cylindrical tolerance zone defined by the DRF using datums A and B. The other notions—being datum-independent, requiring equidistance from the datums, or using a spherical zone—do not reflect how true position is interpreted with two datums.

True position expresses where the feature’s center or axis must lie relative to the datums. When two datums are used, the datum reference frame defined by those datums fixes both the orientation and the location of that axis. The positional tolerance then becomes a cylindrical tolerance zone whose axis aligns with the feature’s true axis and is located by the DRF established from datums A and B. The actual axis must fall inside this cylinder, enforcing the required position in relation to both datums. This is why the correct description is that the true position must lie within a cylindrical tolerance zone defined by the DRF using datums A and B. The other notions—being datum-independent, requiring equidistance from the datums, or using a spherical zone—do not reflect how true position is interpreted with two datums.