The process of comparing an instrument or device with a standard is called:

• A. Alignment
• B. Testing
• C. Verification
• D. Calibration

Answer: (D)

Calibrating an instrument means comparing its readings to a known standard and adjusting the instrument so its output matches that standard within a specified tolerance. This process shows how accurate the measurements are and aligns the instrument’s response with a traceable reference, which is essential for reliable UT readings. In ultrasonic testing, calibration ensures that settings like gain, sensitivity, and velocity produce signals that truly correspond to real material conditions. Alignment, by contrast, is about physically positioning the transducer for consistent scans, not about measurement accuracy. Testing refers to using the instrument to measure or inspect, without addressing its accuracy against a standard. Verification checks that the instrument stays within permitted limits without adjustments. Since calibration directly involves comparing to standards and correcting for any deviation, it is the correct term.