SID indicator accuracy must be within what percentage of the measured value?

• A. +/- 1%
• B. +/- 5%
• C. +/- 2%
• D. +/- 10%

Answer: (C)

SID indicator accuracy refers to how closely the displayed source-to-image distance matches the true distance. This precision matters because image magnification and exposure depend on the actual distance; if the readout is off, you can end up with improper technique, distorted geometry, or inconsistent image quality. The required tolerance is plus or minus 2 percent of the measured SID, a tight margin that keeps magnification calculations reliable and helps maintain consistent dose and positioning across exams. Tolerances like ±1% would be even tougher to achieve; ±5% or ±10% would allow noticeable errors in magnification and exposure, which is not acceptable in controlled radiographic practice.