PDF of this tutorialNowadays humans interact more with computer-based technology than with hammers and drills. Unlike tools, the visible shape and controls of a computer do not communicate its purpose. The task of an HMI is to make the function of a technology self-evident. Much like a well-designed hammer fits the user's hand and makes a physical task easy, a well-designed HMI must fit the user's mental map of the task he or she wishes to carry out.
Figure 1. What Is the Human-Machine Interface?
In nearly every technological solution, the effectiveness of the HMI can predict the acceptance of the entire solution by the intended users. Often, as far as consumers are concerned, the HMI is the product—the user's experience with the interface is far more important than the architecture of the internal workings.
HMI effectiveness is measured by a number of components, such as learnability and productivity. These components are sometimes brought together under the title of "usability," also known as quality of use.
ISO Definition of Quality of Use
The ISO 9241 standard defines three components of quality of use applicable to the design of HMIs:
- effectiveness—Does the product do what the users require? Does it do the right thing?
- efficiency—Can the users learn the HMI quickly? Can they carry out their tasks with minimum expended effort, including a minimum of errors? Does it improve the productivity/effort ratio? Does it do things right?
- satisfaction—Do users express satisfaction with the product? Does the new product reduce stress? Do the end users now have a more satisfying job?
Usability Engineering
These components are not intrinsic qualities of a product. The designer cannot take a tape measure to an HMI and measure its effectiveness, efficiency, 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."
