A method for and apparatus for evaluating the performance of a control system are disclosed. The method includes receiving data from the control system, wherein the data is received by a passive testing function, and calculating a parameter related to the performance of the control system using the passive testing function. The apparatus includes a processor operable to execute a passive testing function, wherein the passive testing function is configured to receive data from the control system and calculate a parameter related to the performance of the control system. The apparatus may also include an active testing function, wherein the active testing function is configured to provide a sequence of step changes to an input of the control system, receive data from the control system in response to the sequence of step changes, and calculate a parameter related to the performance of the control system.