Design of Everyday Things_11

Design of Everyday Things_11 - USER-CENTERED DESIGN .7;—...

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Unformatted text preview: USER-CENTERED DESIGN .7;— ‘ ‘ OFF THE LEASH By W.B. Park @ § § 5 3 3 g a a “Darn these hooves! I hit the wrong switch again! Who designs these instrument panels, raccoons?” 187 The point of POET is to advocate a user-centered design, a philoso- phy based on the needs and interests of the user, with an emphasis on making products usable and understandable. In this chapter I summa— rize the main principles, discuss some implications, and offer sugges- tions for the design of everyday things. Design should: ' Make it easy to determine what actions are possible at any moment (make use of constraints). ' Make things visible, including the conceptual model of the system, the alternative actions, and the results of actions. - Make it easy to evaluate the current state of the system. ° Follow natural mappings between intentions and the required ac- tions,- between actions and the resulting effect; and between the information that is visible and the interpretation of the system state. In other words, make sure that (1) the user can figure out what to do, and (2) the user can tell what is going on. Design should make use of the natural properties of people and of the world: it should exploit natural relationships and natural con- straints. As much as possible, it should operate without instructions or labels. Any necessary instruction or training should be needed only once; with each explanation the person should be able to say, "Of course," or "Yes, I see.” A simple explanation will suffice if there is reason to the design, if everything has its place and its function, and if the outcomes of actions are visible. If the explanation leads the person to think or say, “How am I going to remember that?” the design has failed. Seven Principles for Transforming Difficult Tasks into Simple Ones How does the designer go about the task? As I’ve argued in POET, the principles of design are straightforward. 1. Use both knowledge in the world and knowledge in the head. 2. Simplify the structure of tasks. 3. Make things visible: bridge the gulfs of Execution and Evaluation. 4. Get the mappings right. 188 The Design of Everyday Things 5. Exploit the power of constraints, both natural and artificial. 6. Design for error. 7. When all else fails, standardize. USE BOTH KNOWLEDGE IN THE WORLD AND KNOWLEDGE IN THE HEAD I have argued that people learn better and feel more comfortable when the knowledge required for a task is available extemally—either expli- cit in the world or readily derived through constraints. But knowledge in the world is useful only if there is a natural, easily interpreted relationship between that knowledge and the information it is intended to convey about possible actions and outcomes. Note, however, that when a user is able to internalize the required knowledge—that is, to get it into the head—performance can be faster and more efficient. Therefore, the design should not impede action, especially for those well-practiced, experienced users who have inter- nalized the knowledge. It should be easy to go back and forth, to combine the knowledge in the head with that in the world. Let which- ever is more readily available at the moment be used without interfer- ing with the other, and allow for mutual support. THREE CONCEPTUAL MODELS The operation of any device—whether it be a can opener, a power generating plant, or a computer system—is learned more readily, and the problems are tracked down more accurately and easily, if the user has a good conceptual model. This requires that the principles of opera- tion be observable, that all actions be consistent with the conceptual model, and that the visible parts of the device reflect the current state ‘ of the device in a way consistent with that model. The designer must develop a conceptual model that is appropriate for the user, that cap- tures the important parts of the operation of the device, and that is understandable by the user. Three different aspects of mental models must be distinguished: the design model, the user's model, and the system image (figure 7.1). The design model is the conceptualization that the designer has in mind. The user’s model is what the user develops to explain the operation of the system. Ideally, the user’s model and the design model are equivalent. How- sssz: User-Centered Design 189 @‘é / 2‘ W ever, the user and designer communicate only through the system itself: its physical appearance, its operation, the way it responds, and the manuals and instructions that accompany it. Thus the system image is critical: the designer must ensure that everything about the product is consistent with and exemplifies the operation of the proper concep- tual model. All three aspects are important. The user’s model is essential, of course, for that determines what is understood. In turn, it is up to the designer to start with a design model that is functional, leamable, and usable. The designer must ensure that the system reveals the appropri- ate system image. Only then can the user acquire the proper user’s model and find support for the translation of intentions into actions and system state into interpretations. Remember, the user acquires all knowledge of the system from that system image. 7.1 Three Aspects of Mental Models. The design model, the user’s model, and the system image. (From Norman, 1986.) THE ROLE OF MANUALS The system image includes instruction manuals and documentation. Manuals tend to be less helpful than they should be. They are often Mitten hastily, after the product is designed, under severe time pres- sures and with insufiicient resources, and by people who are over- worked and underappreciated. In the best of worlds, the manuals would be written first, then the design would follow the manual. While the product was being designed, potential users could simultaneously 190 The Design of Everyday Things test the manuals and mock-ups of the system, giving important design feedback about both. Alas, even the best manuals cannot be counted on,- many users do not read them. Obviously it is wrong to expect to operate complex devices without instruction of some sort, but the desigiers of complex devices have to deal with human nature as it is. SIMPLIFY THE STRUCTURE OF TASKS Tasks should be simple in structure, minimizing the amount of plan- ning or problem solving they require. Unnecessarin complex tasks can be restructured, usually by using technological innovations. Here is where the designer must pay attention to the psychology of the person, to the limits on how much a person can hold in memory at one time, to the limits on how many active thoughts can be pursued at once. These are the limitations of short-term and long-term memory and of attention. The limitations of short-term memory (STM) are such that a person should not be required to remember more than about five unrelated items at one time. If necessary, the system should provide technological assistance for any temporary memory requirements. The limitations of long—term memory (LTM) mean that information is bet- ter and more easily acquired if it makes sense, if it can be integrated into some conceptual framework. Moreover, retrieval from LTM is apt to be slow and to contain errors. Here is where information in the world is important, to remind us of what can be done and how to do it. Limitations on attention are also severe; the system should help by minimizing interruption, by providing aids to allow for recovery of the exact status of the operations that were interrupted. A major role of new technology should be to make tasks simpler. A task can be restructured through technology, or technology might pro- vide aids to reduce the mental load. Technological aids can show the alternative courses of action; help evaluate implications; and portray outcomes in a more complete, more easily interpretable manner. These aids can make the mappings more visible or, better, make the mappings more natural. Four major technological approaches can be followed: ' Keep the task much the same, but provide mental aids. ' Use technology to make visible what would otherwise be invisible, thus improving feedback and the ability to keep control. srer: User-Centered Design 191 ' Automate, but keep the task much the same. ' Change the nature of the task. Let us look separately at each of these possibilities. KEEP THE TASK MUCH THE SAME, BUT PROVIDE MENTAL AIDS Don’t underestimate the power or importance of simple mental aids. Consider, for example, the value of simple, everyday notes to our- selves. Without them, we might fail. Or simple notepads for telephone numbers, names, addresses—for the facts that are essential to everyday functioning, but that we cannot trust our own memory structures to provide. Some mental aids are also technological advances; these in- clude watches, timers, calculators, pocket dictating machines, computer notepads, and computer alarms. Some aids are still to come: the pocket computer with a powerful display, which will keep our notes, remind us of our appointments, and smooth our passage through the schedules and interactions of life. USE TECHNOLOGY TO MAKE VISIBLE WHAT WOULD OTHERWISE BE INVISIBLE, THUS IMPROVING FEEDBACK AND THE ABILITY TO KEEP CONTROL ' The instruments in the automobile or aircraft do not change the task, but they do make visible the state of the engine and the other parts of the vehicle, even though you cannot physically get access to them. Similarly, the microscope and telescope, television set, camera, micro- phone, and loudspeaker all provide ways of getting information about a remote object, making visible (or audible) what is happening, making possible tasks and pursuits that would otherwise not be possible. With modern computers and their powerful graphic displays, we now have the power to show what is really happening, to provide a good, com- plete image that matches the person’s mental model of the task—- thereby simplifying both understanding and performance. Today, computer graphics are used more for show than for legitimate pur- poses. Their powers are wasted. But there exists great potential to make visible what should be visible (and to keep hidden what is irrelevant). These first two approaches to mental aids keep the main tasks un- changed. They act as reminders. They reduce memory load by provid- 192 The Design of Everyday Things ing external memory devices (pro viding knowledge in the world rather than requiring it to be in the head). They supplement our perceptual abilities. Sometimes they enhance human skills sufficiently so that a job that was not possible before, or was possible only for the most highly skilled performers, becomes available to many. Don ’t these so-called advances also cause us to lose valuable mental skills? Each technological advance that provides a mental aid also brings along critics who decry the loss of the human skill that has been made less valuable. Fine, I say: if the skill is easily automated, it wasn ’t essential. I prefer to remember things by writing them on a pad of paper rather than spending hours of study on the art of memory. I prefer using a pocket calculator to spending hours of pencil pushing and grinding, usually only to make an arithmetic mistake and not discover it until after the harm has been done. I prefer prerecorded music to no music, even if I risk becoming complacent about the power and beauty of the rare performance. And I prefer writing on a text editor or word proces- sor so that I can concentrate on the ideas and the style, not on making marks on the paper. Then I can go back later and correct ideas, redo the grammar. And with the aid of my all-important spelling correction program, I ' can be confident of my presentation. Do I fear that I will lose my ability to spell as a result of overreliance on this technological crutch? What ability? Actually, my spelling is improving through the use of this spelling corrector that continually points out my errors and suggests the correction, but won ’t make a change unless I approve. It is certainly a lot more patient than my teachers used to be. And it is always there when I need it, day or night. So I get continual feedback about my errors, plus useful advice. My typing does seem to be deteriorating because I can now type even more sloppily, confident that my mistakes will be detected and corrected. In general, I welcome any technological advance that reduces my need for mental work but still gives me the control and enjoyment of the task. That way] can exert my mental efi‘orts on the core of the task, the thing to be remembered, the purpose of the arithmetic or the music. I want to use my mental powers for the important things, not fritter them away on the mechanics. AUTOMATE, BUT KEEP THE TASK MUCH THE SAME There are dangers in simplification: unless we are careful, the auto- mation can harm as well as help. Consider one impact of automation. SEVEM' User-Centered Ups-inn 1oz As before, the task will stay essentially the same, but parts of it will disappear. In some cases the change is confirmed as a universal bless- ing. I don’t know of anyone who misses the automatic spark advance in automobiles or cranking the engine to get it started. Just a few people miss having manual control over the automobile choke. On the whole, this type of automation has resulted in useful advances, replacing tedious or unnecessary tasks and reducing what must be monitored. The automatic controls and instruments of ships and air- craft have been great improvements. Some automation is more prob- lematic. Automatic shift on a car: Do we lose some control, or does it help lighten the mental burden of driving? After all, we drive to get to a destination, so the need to monitor engine speed and gearshift position would seem quite irrelevant. But some people take pleasure in performing the task itself; for them, part of driving is using the engine well, believing that they can operate more efficiently than can the automatic device. What about the automatic pilot of an aircraft, or the automatic navigation systems that have eliminated the sextant and lengthy com- putations? Or what about frozen, precooked meals? Do the changes destroy the essence of the task? Here there’s more debate. In the best of worlds we would be able to choose automation or full control. CHANGE THE NATURE OF THE TASK When a task seems inherently complex because of the manual skill required, certain technological aids can dramatically change which type of skill is required by restructuring the task. In general, technology can help transform deep, wide structures into narrower, shallower ones. Tying a shoelace is one of the standard, everyday tasks that is actu- ally quite difficult to learn. Adults may have forgotten how long it took them to learn (but they will be reminded if their fingers stiffen with injury, age, or disease). The introduction of new fastening materials— for example, Velcro hook-and-loop fasteners—has eliminated the need for a complex sequence of skilled motor actions by changing the task to one that is considerably simpler, one that requires less skill. The task has become possible for both young children and infirm adults. The example of shoelaces may seem trivial, but it isn’t; like many everyday activities, it is difficult for a large segment of the population and its difficulties can be overcome through the restructuring provided by a simple technology. 194 The Design of Everyday Things The hook-and-loop fasteners provide another example of design tradeoffs (figure 7.2). Hook-and-loop fasteners dramatically simplify shoe fastening for the young and infirm. But they add to the problems of parents and teachers, for children delight in fastening and unfasten- ing their shoes; so a fastener that is more difl‘icult to work has certain Virtues. And for sports for which precise support of the foot is required, the best solution still appears to be the shoelace, which can be adjusted so as to ofi‘er difierent tensions at difi‘erent parts of the foot. The current generation of hook-and—loop fasteners does not have the flex- ibility of laces. Digital watches represent another example of how a new technology can supplant an old one; it has delayed or eliminated the need for children to learn the mapping of the analog hands of the traditional clockface onto the hours, minutes, and seconds of the day. Digital timepieces are controversial: in changing the representation of time, the 7.2 Hook-and-Loop Fastener. With the use of hook-and—loop fasteners, the act of tying shoes is much simplified: a good example of the power of technology to change the nature of the task. But there is a cost. Children find the task so easy they gleefully untie their shoes. And these fasteners are not yet as flexible as Shoelaces for the support needed for sports. SEVEN: User-C entered Design 195 power of the analog form has been lost, and it has become more dif- ficult to make quick judgments about time. The digital display makes it easier to determine the exact time, but harder to make estimates or to see approximately how much time has passed since an earlier read- ing. This might serve as a useful reminder that task simplification, by itself, is not necessarily a virtue. I I do not want to argue for digital timepieces, but let me remind you how difl‘icult and arbitrary the analog timepiece really is. After all, it, too, was an arbitrary imposition of a notational scheme, imposed upon the world by the early technologists. Today, because We can no longer remember the origins, we think of the analog system as necessary, virtuous, and proper. It presents a horrid, classic example of the map- ping problem. Yes, the notion that time should be represented by the distance a hand moves around a circle is a good one. The problem is that we use two or three different hands moving around the same circle, each one meaning something different and operating on a different scale. Which hand is which? (Do you remember how hard it is to teach a child the difference between the little hand and the big hand, and not to confuse the second hand—which is sometimes big, sometimes little—With the minute hand or the hour hand?) Do I exaggerate? Read What Kevin Lynch says about this in his delightful book on city planning, What time is this place? "Telling time is a simple technical problem, but unfortunately the clock is a rather obscure perceptual device. Its first widespread use in the thirteenth century was to ring the hours for clerical devotions. The clockface which translated time into spatial alteration, came later. That form was dictated by its works, not by any principle of perception. Two (sometimes three) superimposed cycles give dupli- cate readings, according to angular displacement around a finely marked rim. Neither minutes nor hours nor half days correspond to the natural cycles of our bodies or the sun. And so teaching a child to read a clock is not a childish undertaking. When asked why a clock had two hands, a four-year-old replied, ’God thought it would be a good idea.’ "1 Aircraft designers started using meters that looked like clockfaces to represent altitude. As airplanes were able to fly higher and higher, the meters needed more hands. Guess what? Pilots made errors—seri— ous errors. Multihanded analog altimeters have been largely aban- doned in favor of digital ones because of the prevalence of reading 196 The Design of Everyday Things errors. Even so, many contemporary altimeters maintain a mixed mode.- information about rate and direction of altitude change is determined from a single analog hand, while precise judynents of height come from the digital display. DON'T TAKE AWAY CONTROL Automation has its virtues, but automation is dangerous when it takes too much control from the user. "Overautomation”—too great a degree of automation—has become a technical term in the study of automated aircraft and factories.2 One problem is that overreliance on automated equipment can eliminate a person’s ability to function without it, a prescription for disaster if, for example, one of the highly automated mechanisms of an aircraft suddenly fails. A second problem is that a system may not always do things exactly the way we would like, but we are forced to accept what happens because it is too difficult (or impossible) to change the operation. A third problem is that the person becomes a servant of the system, no longer able to control or influence what is happening. This is the essence of the assembly line: it deper- sonalizes the job, it takes away control, it provides, at best, a passive or third-person experience. All tasks have several layers of control. The lowest level is the details of the operation, the nimble finger work of sewing or playing the piano, the nimble mental work of arithmetic. Higher levels of control affect the overall task, the direction in which the work is going. Here we determine, supervise, and control the overall structure and goals. Auto- mation can work at any level. Sometimes we really want to maintain control at the lower level. For some of us, it is the nimble execution of the finger or mind that matters. Some of us want to play music with skill. Or we like the feel of tools against wood. Or we enjoy wielding a paintbrush. In cases like these, we would not want automation to interfere. At other times we want to concentrate on higher level things. Perhaps our goal is to listen to music, and we find the radio more effective for us than the piano; perhaps our artistic skill can’t get us as far as can a computer program. MAKE THINGS VISIBLE: BRIDGE THE GULFS OF EXECUTION AND EVALUATION This has been a focal theme of POI-3T. Make things visible on the execution side of an action so that people know what is possible and swim: User-Centered Design 107 how actions should be done; make things visible on the evaluation side so that people can tell the effects of their actions. There is more. The system should provide actions that match in- tentions. It should provide indications of system state that are readily perceivable and interpretable and that match intentions and expectations. And, of course, the system state should be visible (or audible) and readily interpretable. Make the outcomes of an action obvious. Sometimes the wrong things are visible. A friend of mine, a profes- sor of computer science at my university, proudly showed me his new CD player and its associated remote control. Sleek, functional. The remote control unit had a little metal loop protruding from one end. When I asked what it was for, my friend told a story. When he first got the set, he assumed that the loop was an antenna for the remote unit, so he always aimed it at the CD player. It didn’t seem to work well,- he had to stand within a few feet of the CD while using the remote. He mumbled to himself that he had bought a poorly designed unit. Weeks later he discovered that the metal hook was just a hook for hanging up the device. He had been aiming the remote at his own body. When he turned the remote around, it worked from far across the room. Here is a case of natural mappings that fails. The hook provided a natural mapping for function: it indicated which side of the remote control device should be poin ted at the CD set. Unfortunately, it pro- vided erroneous information. In making things visible, it is important to make the correct things visible. Otherwise people form explanations for the things they can see, explanations that are likely to be false. And then they find some reason for poor performance—in this example, that the remote was not very po werful. People are very good at forming explanations, at creating mental models. It is the designer’s task to make sure that they form the correct interpretations, the correct mental models.- the system image plays the key role. Remote transmitter units that need to be poin ted at a receiver should have some visible evidence of the transmitting mechanism. Modern ' units carefully hide any indication of the signaling method, violating the rules of visibility. My friend searched hard for some clue of the direction to point the device in, and he found one: the hook. And, no, the instruction manual did not say which end of the unit should be pointed at the CD player. 3 198 The Design of Everyday Things GET THE MAPPINGS RIGHT Exploit natural mappings. Make sure that the user can detemiine the relationships: ° Between intentions and possible actions ' Between actions and their effects on the system - Between actual system state and what is perceivable by sight, sound, or feel ‘ Between the perceived system state and the needs, intentions, and expectations of the user Natural mappings are the basis of what has been called “response compatibility” within the fields of human factors and ergonomics. The major requirement of response compatibility is that the spatial rela- tionship between the positioning of controls and the system or objects upon which they operate should be as direct as possible, with the controls either on the objects themselves or arranged to have an analog- ical relationship to them. In similar fashion, the movement of the controls should be similar or analogous to the expected operation of the system. Difficulties arise wherever the positioning and movements of the controls deviate from strict proximity, mimicry, or analogy to the things being controlled. The same arguments apply to the relationship of system output to expectations. A critical part of an action is the evaluation of its effects. This requires timely feedback of the results. The feedback must pro- vide information that matches the user’s intentions and must be in a form that is easy to understand. Many systems omit the relevant visible outcomes of actions; even when information about the system state is provided, it may not be easy to interpret. The easiest way to make things understandable is to use graphics or pictures. Modern systems (especially computer systems) are quite capable of this, but the need seems not to have been recognized by designers. EXPLOIT THE POWER OF CONSTRAINTS, BOTH NATURAL AND ARTIFICIAL Use constraints so that the user feels as if there is only one possible thing to do—the right thing, of course. In chapter 4 I used the example SEVEN: User-Centered Design 199 of the Lego toy motorcycle, which could be correctly put together by people who had never before seen it. Actually, the toy is not simple. It was carefully designed. It exploits a variety of constraints. It is a good example of the power of natural mappings and constraints, constraints that reduce the number of alternative actions at each step to at most a few. DESIGN FOR ERROR Assume that any error that can be made will be made. Plan for it. Think of each action by the user as an attempt to step in the right direction; an error is simply an action that is incompletely or improperly specified. Think of the action as part of a natural, constructive dialog between user and system. Try to support, not fight, the user’s responses. Allow the user to recover from errors, to know what was done and what happened, and to reverse any unwanted outcome. Make’ it easy to reverse operations; make it hard to do irreversible actions. Design ex- plorable systems. Exploit forcing functions. WHEN ALL ELSE FAILS, STANDARDIZE When something can’t be designed without arbitrary mappings and difficulties, there is one last route: standardize. Standardize the actions, outcomes, layout, displays. Make related actions work in the same way. Standardize the system, the problem; create an international stan- dard. The nice thing about standardization is that no matter how arbi- trary the standardized mechanism, it has to be learned only once. People can learn it and use it effectively. This is true of typewriter keyboards, traffic signs and signals, units of measurement, and calen- dars. When followed consistently, standardization works well. There are difficulties. It may be hard to obtain an agreement. And timing is crucial: it is important to standardize as soon as possible—to save everyone trouble—but late enough to take into account advanced technologies and procedures. The shortcomings of early standardiza- tion are often more than made up for by the increase in ease of use.3 Users have to be trained to the standards. The very conditions that require standardization require training, sometimes extensive training (that is OK: it takes months to learn the alphabet, or to type, or to drive 200 The Design of Everyday Things 7.3 The Backward Clock. (Drawing by Eileen Conway.) a car). Remember, standardization is essential only when all the neces- sary information cannot be placed in the world or when natural map- pings cannot be exploited. The role of training and practice is to make the mappings and required actions more available to the user, overcom- ing any shortcomings in the design, minimizing the need for planning and problem solving. Take the everyday clock. It’s standardized. Consider how much trouble you would have telling time with a back ward clock, where the hands revolved counterclockwise. Such clocks do exist (figure 7.3). They make efiective conversation pieces. Not so good for telling the time, though. Why not? There is nothing illogical about a clock that goes counterclockwise. It’s just as log’cal as one that goes clockwise. The reason we dislike it is that we have standardized on a difi‘erent scheme, on the very definition of the term "clockwise. ” Without such standardization, clock reading would be more dilficult: you’d always have to figure out the mapping. STANDARDIZATION AND TECHNOLOGY If we examine the history of advances in all technological fields, we see that some improvements naturally come through technology, others come through standardization. The early history of the automobile is a good example. The first cars were very difficult to operate. They required strength and skill beyond the abilities of many. Some prob- srsz: User-Centered Design 201 lems were solved through automation: the choke, the spark advance, and the starter engine. Arbitrary aspects of cars and driving had to be standardized: - Which side of the road people drove on - Which side of the car the driver sat on - Where the essential components were: steering wheel, brake, clutch pedal, and accelerator (in some early cars it was on a hand lever) Standardization is simply another aspect of cultural constraints. With standardization, once you have learned to drive one car, you feel justifiably confident that you can drive any car, any place in the world. Today’s computers are still poorly designed, at least from the user’s point of view. But one problem is simply that the technology is still very primitive—like the 1906 auto—and there is no standardization. Standardization is the solution of last resort, an admission that we cannot solve the problems in any other way. So we must at least all agree to a common solution. When we have standardization of our keyboard layouts, our input and output formats, our operating sys- tems, our text editors and word processors, and the basic means of operating any program, then suddenly we will have a major break- through in usability.‘1 THE TIMING OF STANDARDIZATION Standardize and you simplify lives: everyone learns the system only once. But don’t standardize too soon; you may be locked into a primi- tive technology, or you may have introduced rules that turn out to be grossly inefficient, even error-inducing. Standardize too late and there may already be so many ways of doing the task that no international standard can be agreed on; if there is agreement on an old-fashioned technology, it may be too expensive to change. The metric system is a good example: it is a far simpler and more usable scheme for repre- senting distance, weight, volume, and temperature than the older, Brit- ish system (feet, pounds, seconds, degrees on the Fahrenheit scale). But industrial nations with a heavy commitment to the old measurement standards claim they cannot afford the massive costs and confusion of conversion. So we are stuck with two standards, at least for a few more decades. 202 The Design of Everyday Things Would you consider chang'ng how we specify time? The current system is arbitrary. The day is divided into twenty-four rather arbi- trary units—hours. But we tell time in units of twelve, not twenty- four, so there have to be two cycles of twelve hours each, plus the special convention of A.M. and RM. so we know which cycle we are talking about. Then we divide each hour into sixty minutes and each minute into sixty seconds. M’hat if we switched to metric divisions: seconds divided into tenths, milliseconds, and microseconds? We would have days, millidays, and microdays. There would have to be a newhour, minute, and second: call them the newhour, the newminute, and the newsecond. It would be easy.- ten newhours to the day, one hundred newminutes to the newhour, one hundred newseconds to the newminute. Each newhour would last exactly 2.4 times an old hour.- 144 old minutes. So the old one-hour period of the schoolroom or television proyam would be replaced with a half-newhourperiod—only 20 per- cent longer than the old. Each newrninute would be quite similar to the current rru'nute: 0.7 of an old minute, to be exact (each newminute would be about 42 old seconds). And each newsecond would be slightly shorter than an old second. The difi'erences in durations could be gotten used to,- they aren’t that large. And computations would be so much easier. I can hear the everyday conversations now: "111 meet you at noon—5 newhours. Don’t be late, it’s only a half hour from n0w, 50 newminutes, 0K ” "What time is it? 7.85—15 minutes to the evening news. ” What do I think of it? I wouldn ’t go near it. Deliberater Making Things Difficult "How can good design (design that is usable and understandable) be balanced with the need for ’secrecy’ or privacy, or protection? That is, some applications of desigr involve areas which are sensitive and ne- cessitate strict control over who uses and understands them. Perhaps we don’t want any user-in-the-street to understand enough of a sys- tem to compromise its security. Couldn ’t it be argued that some things shouldn’t be designed well? Can ’t things be left cryptic, so that only those who have clearance, extended education, or whatever, can make use of the system? Sure, we have passwords, keys, and other types of ssvmv: User-Centered Design 203 7.4 A School Door, Deliber- ater Made Difficult to Use. The school is for handicapped children; the school officials did not want children to be able to go in and out of the school without adult supervi- sion. The principles of usabil- ity espoused in POET can be followed in reverse to make difficult those tasks that ought to be difficult. security checks, but this can become wearisome for the privileged user. It appears that if good design is not ignored in some contexts, the purpose for the existence of the system will be nullified. "5 Consider figure 7.4, a door on a school in Stapleford, England: the latches are up at the very top of the door, where they are both hard to find and hard to reach. This is good design, deliberately and carefully done. The door is to a school for handicapped children, and the school didn’t want the children to be able to get out to the street without an adult. Violating the rules of ease of use is just what is needed. Most things are intended to be easy to use, but aren’t. But some things are deliberately difficult to use—and ought to be. The number of things that should be difficult to use is surprisingly large: 204 The Design of Everyday Things ' Any door designed to keep people in or out. ' Security systems, designed so that only authorized people will be able to use them. ° Dangerous equipment, which should be restricted. - Dangerous operations, such as life-threatening actions. These can be designed so that one person alone can’t complete the action. I worked for a summer setting off dynamite underwater (to study underwater sound transmission); the circuits were set up to require two people to work them. Two buttons had to be depressed at the same time in order to set off the charge: one button outside, one inside the electronic recording trailer. Similar precautions are taken at military installations. ° Secret doors, cabinets, safes: you don’t want the average person even to know that they are there, let alone to be able to work them. These may require two different keys or combinations, meant to be carried or known by two people. ' Cases deliberately intended to disrupt the normal routine action (in chapter 5 I call these forcing functions). Examples include the ac- knowledgment required before permanently deleting a file from a computer storage system, safeties on pistols and guns, pins in fire extinguishers. ' Controls deliberately made big and spread far apart so that chil- dren will have difficulty operating them. ‘ Cabinets and bottles of medications and dangerous substances deliberately made difficult to open to keep them secure from children. - Games, a category in which designers deliberately flout the laws of understandability and usability. Games are meant to be difficult. And in some games, such as the adventure or Dungeons and Dragons games popular on home (and office) computers, the whole point of the game is to figure out what is to be done, and how. ' No! the door on a train (figure 7.5). Many things need to be designed for a certain lack of understanda- bility or usability. The rules of design are equally important to know here, however, for two reasons. First, even deliberately difficult designs shouldn’t be entirely difficult. Usually there is one difficult part, de- signed to keep unauthorized people from using the device; the rest of it should follow the normal good principles of design. Second, even if your job is to make something difficult to do, you need to know how SEVEN: User-Centered Design 205 to go about doing it. In this case, the rules are useful, for they state in reverse just how to go about the task. You systematically violate the rules. ' Hide critical components: make things invisible. ' Use unnatural mappings for the execution side of the action cycle, so that the relationship of the controls to the things being controlled is inappropriate or haphazard. ' Make the actions physically difficult to do. ' Require precise timing and physical manipulation. ' Do not give any feedback. - Use unnatural mappings for the evaluation side of the action cycle, so that system state is difficult to interpret. Safety systems pose a special problem in design. Oftentimes the design feature added to ensure safety eliminates one danger only to create a secondary one. When workers dig a hole in a street, they must put up barriers to prevent people from walking into the hole. The barriers sol ve one problem, but they themselves pose another danger, often circumvented by adding signs and flashing lights to warn of the barriers. Emergency doors, lights, and alarms must often be accom- panied by warning signs or barriers that control when and how they can be used. Consider the school door of figure 7.4. Under normal use, this design adds to the safety of the children. But what if there was a fire? Even nonhandicapped adults might have trouble with the door as they rushed to get out. What about short or handicapped teachers—how could they open the door? The solution to one problem—unauthorized exit of schoolchildren—can easily create a major new problem in times of fire. How could this problem be solved? Probably with a push bar located within everyone’s reach on the door, but connected to an alarm so that in normal circumstances it would not be used. DESIGNING A DUNGEONS AND DRAGONS GAME One of my students worked for a computer game company helping develop a new Dungeons and Dragons game. He and his fellow stu- dents used his experience to do a class project on the difficulty of 206 The Design of Everyday Things ...
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