Which tolerance describes the annual X-ray symmetry change from baseline?

• A. 2%
• B. Functional
• C. 1%
• D. ±1 mm

Answer: (C)

X-ray symmetry is a measure of how evenly the imaging beam distributes its intensity across the field, and the annual tolerance specifies how much that symmetry is allowed to drift from the baseline over a year. The one percent limit means the current symmetry reading can differ from the baseline by up to one percent; this keeps tracking drift tight enough to catch gradual misalignment without flagging normal small fluctuations as failures. A larger figure like two percent would let more drift slip in, and a measurement in millimeters isn’t the right way to express symmetry, since symmetry is a percentage of even distribution rather than a linear distance. “Functional” doesn’t apply here because this is a numeric tolerance for a quantitative imaging parameter.