What Is the Human-Machine Interface?

iency, or satisfaction scores. Effectiveness depends on the users' intentions, goals, or tasks; efficiency depends on users' understanding of the product and on their previous experience; and satisfaction can only be expressed by the users. As a result, the unifying principle of design techniques that deliver usable products is that each recognizes the need to keep users at the center of the process. The overall design process that brings these techniques together is known as "usability engineering." Usability: Why Is It Important? In an increasingly competitive marketplace, those products and services that do not meet customer needs fail. Ease of use is a real user need and most product reviews, whether in consumer magazines or professional journals, usually compare products based on their usability. Research also shows that about 50% of the code in new software applications is devoted to the user interface, making it a significant cost component. Finally, applications have becom