What technique best helps to find high and low areas on sheet metal?

The technique that best helps to find high and low areas on sheet metal involves running a body file in a diagonal direction. This method is effective because as the file is drawn across the metal surface, it selectively removes material from high spots while leaving low areas untouched. The diagonal motion also helps to highlight discrepancies in the surface, making it easier to identify imperfections.

Body files are specifically designed to smooth out and shape metal surfaces, and using them in a diagonal fashion increases the likelihood of detecting variations in flatness. As the file glides over the surface, the sound and feel of the file will change as it encounters high spots, alerting the technician to areas that need further attention.

Other methods, such as using a straight edge or measuring with calipers, can also be useful in assessing flatness but may not be as immediate or effective in pinpointing the exact locations of high and low areas. Visual inspection can help, but it relies heavily on the observer's ability to detect subtle differences, which may not always be reliable without additional tools or techniques. In contrast, the dynamic action of the body file provides a more tangible and effective means of evaluation.