An indicator is a measurement tool that measures small angles or distances through the process of amplification. Indicators come in a variety of types including dial indicators, digital indicators, test indicators, and probe indicators. Measuring distances and angles that are much too small for the naked eye to discern is made much easier when using an indicator. One example of what an indicator might be used to measure would the difference in thickness of two flat metal slabs. Understanding how to use an indicator properly is important for precise measurement, since the numbers provided by an indicator are based on relative measurements.