Another example of an indicator is a midterm report card. It shows you whether a student is doing well enough to go to the next grade or if extra help is needed. Both of these indicators provide information to help prevent or solve problems, hopefully before they become too severe. Indicators can be useful as proxies or substitutes for measuring conditions that are so complex that there is no direct measurement. For instance, it is hard to measure the 'quality of life in my town' because there are many different things that make up quality of life and people may have different opinions on which conditions count most.
Indicators are quantifiable.
An indicator is not the same thing as an indication, which is generally not quantifiable, but just a vague clue. In addition to being quantifiable, effective indicators have the four basic characteristics noted above. As indicators, the gas gauge and the report card both measure facts that are relevant. If, instead of measuring the amount of gas in the tank, the gas gauge showed the octane rating of the gasoline, it would not help you decide when to refill the tank. Likewise, a report card that measured the number of pencils used by the student would be a poor indicator of academic performance.