Introducing User-Centered Systems Design - Foundations for Designing User-Centered Systems - page 16

Table 1.2 Human characteristics relevant for system design
• Physical characteristics, limitations, and disabilities
• Perceptual abilities, strengths, and weaknesses
• Frequency of product use
• Past experience with same/similar product
• Activity ''mental set'' (the attitude toward and level of motivation you have for the activity)
• Tolerance for error
• Patience and motivation for learning
• Culture/language/population expectations and norms

1.4.1 Anthropometrics Approach

Anthropometrics is concerned with the physical aspects of the user and the system.
For example, Fig. 1.4 shows an input glove. How do people use this? What are
their natural movements in it, and do these movements change with a glove on?
How long can they use it before becoming fatigued or hurt by it? The answers to
questions like these would involve resolving the issues in Table 1.3 .
These physical aspects are often studied in the area of human factors and
ergonomics and applied to standard office equipment like desks and chairs. A lot is
known about how to improve the fit of the hardware to the user's body, including
back, knees, waist, and arms (Pheasant and Haslegrave 2006 ). The optimal work
surface height, for example, varies by the individual concerned but also by the task
to be performed.
It is also important that we consider whether we need to design for individuals
(e.g., desk setups need to be specifically tailored to avoid upper limb disorders), for
the average (e.g., seats in buses and trains are designed for averages), or for
extremes (e.g., plane ejector seats). For example, Ted Williams, the famous
American baseball player and fighter aircraft pilot, reportedly crash-landed a plane
rather than eject so that he would be able to play baseball again after the Korean
war—the design error was that ejector seats were designed for the average height
of a pilot, which left those in the upper 5-10% of the height range in danger of
damaged or removed kneecaps if they ejected. 1
In computer systems these problems include making sure that controls (knobs,
dials, buttons, and so on) are of a size that can be manipulated by a wide range of
users. Weight and button size are important for their usability and the perceived
usability for their marketing. For example, the release of many different sizes of
interactive tablet computers into the market over recent years suggests the physical
sizes of these devices matter for different use scenarios. Early mobile phones were

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