Standards govern many traffic situations drive on

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standards govern many traffic situations: Drive on only one side of the street. The first car into an intersection has precedence. If both arrive at the same time, the car on the right (or left) has precedence. When merging traffic lanes, alternate cars one from that lane, then one from this. The last rule is more of an informal convention: it is not part of any rule book that I am aware of, and although it is very nicely obeyed in the California streets on which I drive, the very concept would seem strange in some parts of the world. Sometimes conventions clash. In Mexico, when two cars approach a narrow, one-lane bridge from opposite directions, if a car 132 The Design of Everyday Things blinks its headlights, it means, I got here first and I m going over the bridge. In England, if a car blinks its lights, it means, I see you: please go first. Either signal is equally appropriate and useful,
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but not if the two drivers follow different conventions. Imagine a Mexican driver meeting an English driver in some third country. (Note that driving experts warn against using headlight blinks as signals because even within any single country, either interpretation is held by many drivers, none of whom imagines someone else might have the opposite interpretation.) Ever get embarrassed at a formal dinner party where there appear to be dozens of utensils at each place setting? What do you do? Do you drink that nice bowl of water or is it for dipping your fingers to clean them? Do you eat a chicken drumstick or slice of pizza with your fingers or with a knife and fork? Do these issues matter? Yes, they do. Violate conventions and you are marked as an outsider. A rude outsider, at that. Applying Affordances, Signifiers, and Constraints to Everyday Objects Affordances, signifiers, mappings, and constraints can simplify our encounters with everyday objects. Failure to properly deploy these cues leads to problems. THE PROBLEM WITH DOORS In Chapter 1 we encountered the sad story of my friend who was trapped between sets of glass doors at a post office, trapped because there were no clues to the doors operation. To operate a door, we have to find the side that opens and the part to be manipulated; in other words, we need to figure out what to do and where to do it. We expect to find some visible signal, a signifier, for the correct operation: a plate, an extension, a hollow, an indentation something that allows the hand to touch, grasp, turn, or fit into. This tells us where to act. The next step is to figure out how: we must determine what operations are permitted, in part by using the signifiers, in part guided by constraints. four: Knowing What to Do: Constraints, Discoverability, and Feedback 133 Doors come in amazing variety. Some open only if a button is pushed, and some don t indicate how to open at all, having neither buttons, nor hardware, nor any other sign of their operation.
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