TMART checks performance, availability and accuracy through different steps.
For example, any webpage is monitored through the TMART. In the Central UI it will show the health screen of that montior. That's is the performance.
For a certain period of time the monitored webpage is responding properly, then it is available.
Only if the webpage the available , the accuracy is checked.
Performance is a number between 0 and 100, with 100 meaning fast performance .According to historical measurements or established standards.