What is a datum line?

• A. A reference point used for measuring vehicle alignment
• B. A line on the paint chip for color matching
• C. A mark indicating bumper height
• D. A scale used for wheel torque

Answer: (A)

A datum line is a fixed reference line used for measuring vehicle alignment. It provides a baseline from which you compare positions of the frame, panels, and other structural points to determine if the car’s geometry matches the manufacturer’s specifications. Having this consistent reference lets technicians take repeatable, accurate measurements, which is essential when assessing damage, checking straightness, and guiding repairs. It isn’t about color matching, bumper height, or wheel torque—those are different concepts. The datum line keeps measurements consistent across the repair process.