What is the difference between 'true position' and 'actual position'?

• A. True position is the theoretical target; actual position is the measured position.
• B. True position is measured; actual position is theoretical.
• C. They are the same.
• D. True position is the centerline; actual position is the edge.

Answer: (A)

In this topic, the key idea is how a feature’s location is defined versus what is actually measured. The true position is the theoretical target location of the feature, set by the datums and basic dimensions—it's the ideal coordinate the part should achieve. The actual position is what’s observed when you measure the part—the real location of the feature center after manufacturing.

During inspection, you compare the measured actual position to the true position to see if the feature lies within the allowed tolerance zone. If the measured position falls inside that zone, the part passes; if not, it’s out of tolerance.

So the correct understanding is that true position is the theoretical target, and actual position is the measured position. The other descriptions mix up which is target and which is observed, or mislabel the concepts (for example, defining true position as the centerline or as the edge).