In machining, what is the purpose of using a dial indicator?

Using a dial indicator is particularly important in checking surface flatness because it allows for precise measurement of deviations from a flat plane. This tool consists of a dial with a pointer that moves in response to a plunger making contact with a surface. When the plunger contacts the surface, any variations in height can be detected, and the dial measures these variations in thousandths of an inch. This precision is crucial in engine construction and installation, as any uneven surfaces can affect the mating of components, ultimately impacting performance and durability.

While dial indicators can also be used for other tasks such as those listed in the other options, their primary and most common use in machining contexts is to ensure that surfaces are flat, enabling effective and accurate assembly of engine components.