Which equipment is used to measure the “flatness” of a milled surface?

A height gauge or surface plate is ideally suited for measuring the flatness of a milled surface due to its design and functionality. Height gauges are precision instruments that can determine vertical distances and are often used in conjunction with a surface plate, which is a flat reference surface. By placing the milled part on the surface plate, the height gauge can measure variations in height across different points of the workpiece, enabling the operator to identify any imperfections or irregularities in flatness.

The importance of using this combination lies in the precision required for measuring flat surfaces. The surface plate itself provides a stable and known reference for the measurements, ensuring that any deviations in flatness can be accurately detected.

In contrast, other tools such as a level gauge primarily check for horizontal alignment rather than flatness across a surface. A digital caliper is great for measuring dimensions and thickness but not specifically designed for assessing surface flatness. A protractor is used for measuring angles and would not provide meaningful measurements related to a surface's flat characteristics. Hence, the height gauge and surface plate represent the most appropriate choices for this specific measurement task.