Politely pointed out that the proper design

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politely pointed out that the proper design principles to avoid these errors had been known for fifty years. Why were these design errors still being made? Basic switches and controls should be relatively simple to design well. But there are two fundamental difficulties. The first is to determine what type of device they control; for example, flaps or landing gear. The second is the mapping problem, discussed extensively in Chapters 1 and 3; for example, when there are many 136 The Design of Everyday Things lights and an array of switches, which switch controls which light? The switch problem becomes serious only where there are many of them. It isn t a problem in situations with one switch, and it is only a minor problem where there are two switches. But the difficulties mount rapidly with more than two switches at the same location. Multiple switches are more likely to appear in offices, auditoriums, and industrial locations than in homes. With complex installations, where there are numerous lights and switches, the light controls seldom fit the needs of the situation. When I give talks, I need a way to dim the light hitting the projection screen so that images are visible, but keep enough light on the audience so that they can take notes (and I can monitor their reaction to the talk). This kind of control is seldom provided. Electricians are not trained to do task analyses. Whose fault is this? Probably nobody s. Blaming a person is seldom appropriate or useful, a point I return to in Chapter 5. The problem is probably due to the difficulties of coordinating the different professions involved in installing light controls. FIGURE 4.4. Incomprehensible Light Switches. Banks of switches like this are not uncommon in homes. There is no obvious mapping between the switches and the lights being controlled. I once had a similar panel in my home, although with only six switches. Even after years of living in the house, I could never remember which to use, so I simply put all the switches either up (on) or down (off). How did I solve the problem? See Figure 4.5. four: Knowing What to Do: Constraints, Discoverability, and Feedback 137 I once lived in a wonderful house on the cliffs of Del Mar, California, designed for us by two young, award-winning architects. The house was wonderful, and the architects proved their worth by the spectacular placement of the house and the broad windows that overlooked the ocean. But they liked spare, neat, modern design to a fault. Inside the house were, among other things, neat rows of light switches: A horizontal row of four identical switches in the front hall, a vertical column of six identical switches in the living room. You will get used to it, the architects assured us when we complained. We never did. Figure 4.4 shows an eight-switch bank that I found in a home I was visiting. Who could remember what each does? My home only had six switches, and that was bad enough. (Photographs of the switch plate from my Del Mar home are no longer available.)
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