In Chapter 3, we outlined a basic method for system design used by human factors specialists to enhance system effectiveness and safety. In HCI, a similar design method is used. In the design sequence, the critical components include (2) involvement of typical users throughout the design lifecycle to be sure their needs are understood, (2) use of guidelines and principles in design, and (3) iterative usability testing beginning early in the design process. While there are many models for software interface design, most include steps such as those suggested by Mayhew (1992). One important aspect of the design process is that users should be heavily involved.