Relevant: It measures an important part of an objective or output;
Objective: If two people measure the same indicator using the same tool, they should get the same result. The indicator should be based on fact, rather than feelings or impressions (another way to say this is to say that it should be Measurable);
Available: Indicators should be based on data that is readily available, or on data that can be collected with reasonable extra effort as part of the implementation of the (sub-) project.
Realistic: It should not be too difficult or too expensive to collect the information (related to the next one in the list);
Specific: The measured changes should be attributable to the project, and they should be expressed in precise terms
