Why is a basic dimension used with a true position tolerance?

Why is a basic dimension used with a true position tolerance?

• A. It defines the exact target location for the feature whose position is being controlled.
• B. It defines the size of the tolerance zone.
• C. It specifies the datum reference frame order.
• D. It sets the material condition modifier.

Answer: (A)

Basic dimensions provide the exact target location for a feature’s position. The true position tolerance then defines how far the actual feature can deviate from that target. Since a basic dimension is exact (no tolerance), it fixes the theoretical point or pattern where the feature must lie, and the true position tolerance encircles that fixed target with the allowable zone. Without that precise target from the basic dimension, there would be nothing to compare the real feature location against. The other ideas relate to how big the tolerance zone is (set by the tolerance value itself), how the reference frame is established (datum order), or how size conditions affect the feature (material condition modifier)—none of which establish the exact target location used by the true position tolerance.

Basic dimensions provide the exact target location for a feature’s position. The true position tolerance then defines how far the actual feature can deviate from that target. Since a basic dimension is exact (no tolerance), it fixes the theoretical point or pattern where the feature must lie, and the true position tolerance encircles that fixed target with the allowable zone. Without that precise target from the basic dimension, there would be nothing to compare the real feature location against. The other ideas relate to how big the tolerance zone is (set by the tolerance value itself), how the reference frame is established (datum order), or how size conditions affect the feature (material condition modifier)—none of which establish the exact target location used by the true position tolerance.