For SID 60 inches, the central ray alignment error should be 1% of SID. What is this distance in inches?

For SID 60 inches, the central ray alignment error should be 1% of SID. What is this distance in inches?

• A. 0.3 inches
• B. 0.6 inches
• C. 1.2 inches
• D. 3.0 inches

Answer: (B)

Understanding how a 1% tolerance for central ray alignment translates into a physical distance at a given SID is the key idea. You multiply the SID by 0.01 to find the allowable misalignment. For a SID of 60 inches, that’s 60 × 0.01 = 0.60 inches. So the central ray alignment error should be about 0.6 inches. The other options correspond to different fractions of SID (0.3 inches is 0.5%, 1.2 inches is 2%, and 3.0 inches is 5%), which exceed or fall short of the 1% criterion.

Understanding how a 1% tolerance for central ray alignment translates into a physical distance at a given SID is the key idea. You multiply the SID by 0.01 to find the allowable misalignment. For a SID of 60 inches, that’s 60 × 0.01 = 0.60 inches. So the central ray alignment error should be about 0.6 inches. The other options correspond to different fractions of SID (0.3 inches is 0.5%, 1.2 inches is 2%, and 3.0 inches is 5%), which exceed or fall short of the 1% criterion.