Abstract: It has been recognized that to improve the usability of diagnostic systems and software, such a system can be designed to step the user through a systematic diagnosis of a problem. The process of systematically stepping through the diagnosis can be designed to teach the user how the system operates. In the result, as users gain more knowledge about how the control system operates they can become more efficient at solving problems independently of the diagnostics software. A methodology is utilized which incorporates a hierarchy of conditions in order to drill down into a problem by making one or more simple queries that can be understood without special skills or training.