Testability has been introduced as a subset of maintainability. It was defined as a design characteristic that allows the status of an item to be determined and faults to be detected and isolated efficiently (or at an "affordable" cost). Diagnostics consists of the manual, automatic, and semi-automatic maintenance hardware,software, and procedures used to determine status, detect faults, and isolate faults. The required hardware, software, and procedures will depend in large measure on the maintainability of the design (i.e., testability characteristics). Diagnostics are just one aspect of maintenance. All maintenance procedures are determined in large measure by the design. A highly maintainable design will require the least amount of support equipment and the fewest and the simplest procedures.