Indicators are simple measures that provide information about complex systems. Some popular economic indicators are Gross Domestic produce (GDP) and the Dow Jones Index for the sharemarket. indicators of health are, for example, body temperature, cholesterol level, blood pressure and pulse rate. Indicators gain their meaning and significance from the interpretive theory built up around them: standards, acceptable levels, trends, norms etc. For instance, a high temperature indicates that a person is sick because we know that the body reacts to certain diseases by producing extra heat. In order to diagnose the disease, however, another set of indicators is needed.