Which of the following best describes the function of a dial indicator?

The function of a dial indicator is to measure small distances and variations with a high degree of precision. It is commonly used in machining and alignment tasks to detect minute changes in dimensions, such as surface flatness, runout of rotating parts, and the alignment of machine components. The dial indicator translates these small movements into a dial reading, allowing operators to monitor and adjust positions accurately.

While checking the flatness of surfaces can be a function of a dial indicator (which might make option B tempting), its broader primary purpose is to measure small distances and variations across various applications beyond just flatness. This versatility is what makes dial indicators critical tools in precision machining and setup tasks.