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`Apple Inc.
`Exhibit 1016
`Page 001
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`

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` ”WWW> r7“.
`
`THE
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`PSYCHOLOGY
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`OF EVERYDAY
`
`THINGS
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`Donald A. Norman
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`BASIC
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`,
`B006
`A Member of The Perseus Books Group
`
`Apple Inc.
`Exhibit 1016
`Page 002
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`

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`Library of Congress Catalogingdn-Publication Data
`Norman, Donald A.
`The psychology of everyday things.
`Includes index.
`
`1. Design, industrial—Psychological aspects.
`2. Human engineering.
`I. Title.
`87-47782
`TS1714.N67 1988
`620.8":
`ISBN—10: 0—465-06709-3
`ISBN-13: 978-0-465-06709—1
`
`Copyright © 1988 by Donald A. Norman
`Printed in the United States of America
`Designed by Barbara DuPree Knowles
`
`
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`
`
`CONTENTS
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`ONE:
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`TWO:
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`[I'IREEZ
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`FOUR 1
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`SIX:
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`SEVEN:
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`Preface
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`The Psychopathology of Everyday Things
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`The Psychology of Everyday Actions
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`Knowledge in the Head and in the World
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`Knowing What to Do
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`To Err Is Human
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`The Design Challenge
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`User-Centered Design
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`Notes
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`Suggested Readings
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`References
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`Index
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`34
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`54
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`81
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`105
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`141
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`187
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`2.19
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`237
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`241
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`249
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`Apple Inc.
`Exhibit 1016
`Page 003
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`

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`CHAPTER ONE
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`THE
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`PSYCHOPATHOLOGY
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`OF EVERYDAY
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`THINGS
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`”You would need an engineering degree from MIT to work this,”
`someone once told me, shaking his head in puzzlement over his brand
`new digital watch. Well, I have an engineering degree from MIT.
`(Kenneth Olsen has two of them, and he can't figure out a microwave
`oven.) Give me a few hours and I can figure out the watch. But why
`should it take hours? I have talked with many people who can’t use all
`the features of their washing machines or cameras, who can’t figure out
`how to work a sewing machine or a video cassette recorder, who
`habitually turn on the wrong stove burner.
`Why do we put up with the frustrations of everyday objects, with
`objects that we can't figure out how to use, with those neat plastic-
`wrapped packages that seem impossible to open, with doors that trap
`people, with washing machines and dryers that have become too con-
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`q
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`a4
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`”Kenneth Olsen, the eng'neer who founded and
`still runs Digital Equipment Corp, confessed at
`the annual meeting thathe can ’1‘ figure authow to
`heat a cup of cofl'ee in the company’s microwave
`oven. ”1
`
`'
`'
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`You Would Need an Engineering Degree
`to Figure This Out
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`Apple Inc.
`Exhibit 1016
`Page 004
`
`

`

`l
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` opening doors?” Yes. I push doors that are meant to be pulled, pull
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`doors that should be pushed, and walk into doors that should be slid.
`Moreover, I see others having the same troubles—unnecessary trou-
`bles. There are psychological principles that can be followed to make
`these things understandable and usable.
`Consider the door. There is not much you can do to a door: you can
`open it or shut it. Suppose you are in an office building, walking down
`a corridor. You come to a door. In which direction does it open? Should
`you pull or push, on the left or the right? Maybe the door slides. If so,
`in which direction? I have seen doors that slide up into the ceiling. A
`door poses only two essential questions: In which direction does it
`move? On which side should one work it? The answers should be given
`by the design, without any need for words or symbols, certainly with-
`out any need for trial and error.
`
`sion of the artist.
`
`1.1 Carelman’s Coffeepot for Maso-
`chists. The French artist Jacques Carel-
`man in his series of books Catalogue
`d'abjrfs inh‘aumzbles {Catalog of unfindable alr—
`jerls) provides delightful examples of
`everyday things that are deliberately
`unworkable, outrageous, or otherwise
`ill-formed. Jacques Carelrnan:
`"Cof—
`feepot for Masochists.” Copyright ©
`1969—76—80 by Jacques Carelman and
`A. D. A. G. P. Paris. From Jacques Carel-
`rnan, Catalog of Unfindnble Objects, Balland,
`éditeur, Paris-France. Used by permis-
`
`fusing to use, with audio-stereo-television—video-cassette-recorders
`that claim in their advertisements to do everything, but that make it
`almost impossible to do anything?
`The human mind is exquisitely tailored to make sense of the world.
`Give it the slightest clue and off it goes, providing explanation, ration-
`alization, understanding. Consider the objects—books, radios, kitchen
`appliances, office machines, and light switches—that make up our ev—
`eryday lives. Well-designed objects are easy to interpret and under—
`stand. They contain visible clues to their operation. Poorly designed
`objects can be diffith and frustrating to use. They provide no Clues-—
`or sometimes false clues. They trap the user and thwart the normal
`process of
`interpretation and understanding. Alas, poor design
`predominates. The result is a world filled with frustration, with objects
`that cannot be understood, with devices that lead to error. This book
`is an attempt to change things.
`
`The Frustrations
`
`of Everyday Life
`
`A friend told me of the time he got trapped in the doorway ofa post
`ofi‘ice in a European city. The entrance was an imposingrow ofperhaps
`six glass swinging doors, followed immediately by a second, identical
`row. That’s a standard deSign: it helps reduce the airflow and thus
`maintain the indoor temperature of the building.
`My friend pushed on the side of one of the leftmost pair of outer
`doors. It swung inward, and he entered the building. Then, before he
`couldget to the nextrOW ofdoors, he was distracted and turned around
`foran instant. He didn ’t realize it at the time, buthe had moved slightly
`to the right. So when he came to the next door and pushed it, nothing
`happened. ”HD1111, ” he thought, ”mustbe locked.” So he pushed the
`side of the adjacent door. Nothing. Puzzled, my friend decided to go
`outside again. Hetumed around andpushed against the side ofa door.
`Nothing. He pushed the adjacent door. Nothing. The door he hadjust
`entered no longer worked. He turned around once more and tried the
`inside doors again. Nothing. Concern, then mildpanic. He was trapped!
`just then, a group ofpeople on the other side of the entranceway (to
`my friend’5 right) passed easilythrough both sets of doors. My friend
`hurried over to follow their path.
`HOW could such a thing happen? A swiny‘ng door has two sides.
`One contains the supporting pillar and thelu’nge, the other is unsup-
`ported. To open the door, you must push on the unsupported edge. If
`you push on the hinge side, nothing happens. In this case, the designer
`aimed for beauty, not utility. No distracting lines, no visible pillars, no
`Visible hinges. So how can the ordinary user know which side to push
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`[f I were placed in the cockpit of a modern jet airliner, my inability to
`perform gracefully and smoothly would neither surprise nor bother me.
`But I shouldn’t have trouble with doors and switches, water faucets
`and stoves. ”Doors?” I can hear the reader saying, ”you have trouble
`
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`Apple Inc.
`Exhibit 1016
`Page 005
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`

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`1.2, A Row of Swinging Glass Doors in a Boston Hotel. A similar problem to
`the doors from that European post office. On which side of the door should you
`push? When i asked people'who had just used thedoors, most couldn’t say. Yet
`only a fewof the people I watched had trouble with the doors. The designers had
`incorporated a subtle clue into the design. Note that the horizontal bars are not
`centeredz" they are atbit closer together on the sides you should push on. The design
`almost works—but not entirely, for not everyone used the‘doors right on the first
`try.
`
`on? While dish-acted my fir‘e’nd had moved toward the (invisible)
`supportingpillar, so he was pushing the doors on the hinged side. No
`wonder nothing happened. Pretty doors. Elegant. Probably Won a de-
`sign pu'ze.
`‘
`‘
`
`The door story illustrates one of the most important principles of
`design: visibility. The correct parts must be visible, and they must con—
`vey the correct message. With doors that push, the designer must
`provide signals that naturally indicate where to push. These need not
`destroy the aesthetics. Put a vertical plate on the side to be pushed,
`nOthing on‘the other. Or make the supporting pillars visible;Th‘e
`vertical platel‘and supporting pillars are natural signals, naturally inter-
`preted, without any‘ need to be conscious of them. I call the use of
`natural signals natural design and elaborate on the approach throughout
`this book.
`'
`'
`‘
`"
`
`Visibility problems come in many forms. My friend, trapped be-
`, tween the glass doors, suffered from a lack of clues that would indicate
`what part of a door should be operated. Other problems concern the
`mappings between what you want to do and what appears to be possible,
`another topic that will be expanded upon throughout the book. Con-
`sider one type of slide projector. This projector has a single button to
`control whether the slide tray moves forward or backward. One button
`to do two things? What is the mapping? How can you figure out how
`to control the slides? You can't. Nothing is visible to give the slightest
`hint. Here is what happened to me in one of the many unfamiliar places
`I've lectured in during my travels as a professor:
`
`The Leitz slide projector illustrated in figure I.3 has shown up sev-
`eral times in my travels. The first time, it led to a rather dramatic
`incident A conscientious student was in charge ofshowing my slides.
`I started my talk and showed the first slide. When I finished with the
`first slide and asked for the next, the student carefully pushed the
`control button and watched in dismay as the tray backed up, slid out
`of the projector and plopped 019r the table onto the floor, spilling its
`entire contents. We had to delay the lecture fifteen minutes while I
`struggled to reorganize the slides. It wasn’t the student’s fault. It was
`
`the fault of the elegant projector. With only one button to control the
`slide advance, how could one switch from forward to reverse? Neither
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`of us could figure out how to make the control work.
`All during the lecture the slides would sometimes go forward, some—
`times backward. Afterward, we found the local technician, who ex-
`plained it to us. A brief push of the button and the slide would go
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`Taste (7) fiir Diawechsel am Ger-5t
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`Diawechsel vorwarts = kurz driicken,
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`Diawechsel riickwartz = l‘a'n’ger drucken.
`'
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`Button (7) for changing the slides
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`Slide change forward = short press,
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`Slide change backWard ‘= longer press.
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`1.3 Leitz Pravodit Slide
`Projector.
`I
`finally tracked
`down the instruction manual
`for that projector. A photoé
`graph of the projector has its
`parts numbered. The button
`for changing slides is number
`7. The button itself has no la-
`bels. Who could discover this
`operation without the aid of
`the manual? Here is the entire
`text related to the button, in
`the original German and in my
`English translation:
`
`Apple Inc.
`Exhibit 1016
`Page 006
`
`

`

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`forward, a long push and it would reverse. (Pity the conscientious
`student who kept pushing it hard—and long—to make sure that the
`stretch was making contact.) What an elegant design. Why, it managed
`to do two functions with only one button! But how was a first-tinIe
`user of the projector to know this?
`
`'As another example, consider the beautiful Amphitheatre Louis—
`Laird in the Paris Sorbonne,"which is filled with magnh‘icentpaintirrgs
`ofgreat figures in French intellectUal history. (The mural 0n the ceiling
`shOWs lbts of naked women floating about a "man who is valiantly
`trying to read a book. The painting is right side up only for the lec-
`turera—it is upside down for all thepeople in the audience.) The room
`is a delight to lecture in, at least until you ask for the projection screen
`to be lowered. ”Ah,”says the professorin charge, who gestures to the
`technician, who runs out Of the room, up a short flight of stairs, and
`out of’sight behind .a solid wall. The screen comes dawn and stops.
`’No, no, ” shouts the professor, ”a little bit more. ” The screen comes
`down again, this time too much. ’No, no, no!” the professorjumps up
`and dawn andgestures wildly. It’s a lovelyroo , with lovelypaintings.
`But why can’t the person who is trying to lower or raise the screen see
`what he is doing?-
`'
`‘
`T
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`New telephone systems have proven to be ”another excellent exam—
`ple‘ of incomprehensible design. No matter where I travel, I Can count
`upon finding a particularly'bad example.
`‘
`‘
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`When I visited Basic Books, the publishers of this book, I noticed a
`new telephone system. Iaskedpeople how they liked it. The question
`unleashed a torrent of abuse. ”It doesn’t have a hold function,” one
`woman complained bitterly—the same complaintpeople at my univer-
`sity made about their rather difl‘erent system. In older days, business
`phones always hada button labeled ”hold. ” You couldpush the button
`and hang up the phone without losing the call on your line. Then you
`could talk to a colleagueorpick up another telephone call, or even pick
`up the call at anotherphone with the same telephone number. A light
`on the hold button indicated when the function was in Use. It was an
`invaluable toolfor'business. Why didn’t the newphones atBasic Books
`orin‘my universityhave a holdfunction, ifitis so‘essential? Well, they
`did, even the very instrument the woman wascomplaining about. But
`there Was no easy way to discover the fact, nor to learn how to use itl
`I was visiting the University oflVIichigan and Iasked about the new I
`
`1.4 Plate Mounted Over the
`Dial of the Telephones at
`the University of Michigan. *
`These inadequate instructions
`are all
`that most users see.
`(The button labeled ”TAP” at
`the lower
`right
`is used to
`transfer or pick up calls—it is
`pressed whenever the instruc~
`‘fion plate says “TAP.” The
`light on the lower left comes
`on whenever
`the telephone
`\
`rings-J
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`system there. "Yeah!” was the response, ' "and it doesn’t even have a
`hold function!” Here we go again. What is going on? The answer is
`simple: firsb‘look at the instructions for hold. At the University of
`Mchrgan the phane Companyprovided a little plate that tits over the
`keypad and reminds users of the functions and how to use them. I
`carefully unhooked one of the plates from the telephone and made a
`photocopy (figure 1.4). Can you understand how to use it? I can’t.
`There is a f’call hold” operation, but it doesn’t make sense to me, not
`for the application that Ijust described.
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`‘ The telephOne hold situation illustrates a number of different prob—
`ilems. One of them is silnply poor instructions, especially a failure to
`relate the new functions 'to the similarly named functions that, people
`already know about. Second, and more serious, is the lack of visibility of
`the operation of the system. The new telephones, for all their added
`sophistication, lack both the hold button and the flashing light of the old
`ones. The hold is signified by an arbitrary action: dialing an arbitrary
`sequence of digits (*8, or *99, or What have you: it varies from one
`phone system to another). Third, there is no visible Outcome of the
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`’ operation.
`Devices in'the home have developed some related problems: func-
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`tions and more functions, controls and ’more controls. I do not think
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`ytha’c‘simple home applianceséstoves, Washing machines, audio and
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`1‘television sets—should look like Hollywood’s idea of a spaceship con-
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`lrol room.They already do, much to the Consternatio‘n of the consumer
`_
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`: ’Who, often as not, has lost (or cannot understand) the instruction
`
`
`
`Apple Inc.
`Exhibit 1016
`Page 007
`
`

`

`manual, so—faced with the bewildering array of controls and dis-
`plays—simply memorizes one or two fixed settings to approximate
`what is desired. The whole purpose of the design is lost.
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`
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`In England I visited a home with a fancy new Italian washer-drier
`combination, with super-dupermulti—symbol controls, all to do every—
`thing you ever wanted to do with the washing and drying of clothes.
`The husband (an engzneenng psychologist) said he refused to go near
`it. The wife (a physician) said she had simply memorized one setting
`and tried to ignore the rest.
`Someone went to a lot of trouble to create that design. I read the
`instruction manual. That machine took into account everything about
`today’s wide variety of synthetic and natural fabrics. The designers
`worked hard,- they really cared. But obviously they had never thought
`of trying it out, or of watching anyone use it.
`If the design was so bad, if the controls were so unusable, why did
`the couple purchase it? If people keep buying poorly designed pro—
`ducts, manufacturers and designers will think they are doing the right
`thing and continue as usual.
`
`The user needs help. Just the right things have to be visible: to
`indicate what parts operate and how, to indicate how the user is to
`interact with the device. Visibility indicates the mapping between in—
`tended actions and actual operations. Visibility indicates crucial dis-
`tinctions—so thatyou can tell salt and pepper shakers apart, for exam-
`ple. And visibility of the effects of the operations tells you if the lights
`have turned on properly, if the projection screen has lowered to the
`correct height, or if the refrigerator temperature is adjusted correctly.
`It is lack of visibility that makes so many computer-controlled devices
`so difficult to operate. And it is an excess of visibility that makes the
`gadget—ridden, feature-laden modern audio set or video cassette re-
`corder (VCR) so intimidating.
`
`The Psychology
`of Everyday Things
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`This book is about the psychology of everyday things. POET empha-
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`sizes the understanding of everyday things, things with knobs and
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`dials, controls and switches, lights and meters. The instances we have
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`just examined demonstrate several principles, including the importance
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`of visibility, appropriate clues, and feedback of one’s actions. These
`principles constitute a form of psychology—the psychology of how
`people interact with things. A British designer once noted that the
`kinds of materials used in the construction of passenger shelters af-
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`fected the way vandals responded. He suggested that there might be
`a psychology of materials.
`
`AFFORDANCES
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`”In one case, the reinforced glass used to panel shelters {for railroad
`passengers) erected by British Rail was smashed by vandals as fast as
`it was renewed. When the reinforced glass was replaced by plywood
`boarding, however, little further damage occurred, although no extra
`force would have been required to produce it. Thus British Rail
`managed to elevate the desire for defacement to those who could write,
`albeit in somewhat limited terms. Nobody has, as yet, considered
`Whether there is a kind ofpsychology ofma terials. But on the evidence,
`there could well be!”2
`
`There already exists the start of a psychology of materials and of
`things, the study of affordancesof objects. When used in this sense,
`the term aiora'ance refers to the perceived and actual properties of the
`thing, primarily those fundamental properties that determine just how
`the thing could possibly be used (see figures 1.5 and 1.6). A chair
`affords (”is for”) support and, therefore, affords sitting. A chair can also
`be carried. Glass is for seeing through, and for breaking. Wood is
`normally used for solidity, opacity, support, or carving. Flat, porous,
`smooth surfaces are for writing on. So wood is also for writing on.
`Hence the problem for British Rail: when the shelters had glass, van-
`dals smashed it; when they had plywood, vandals wrote on and carved
`it. The planners were trapped by the affordances of their materials.3
`Affordances provide strong clues to the operations of things. Plates
`are for pushing. Knobs are for turning. Slots are for inserting things
`into. Balls are for throwing or bouncing. When affordances are taken
`advantage of, the user knows what to do just by looking: no picture,
`label, or instruction is required. Complex things may require explana-
`tion, but simple things should not. When simple things need pictures,
`labels, or instructions, the design has failed.
`A psychology of causality is also at work as we use everyday things.
`
`9
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`Apple Inc.
`Exhibit 1016
`Page 008
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`

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`1.5 Affordances of D001‘8.‘Door hardware can signal whether topush or pull
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`without signs The flat horizontal bar of A (above left) affords no operations except
`pushing: it is excellent hardware for a docir that must be pushed to be opened. The
`door in B (above right) has a different kind of bar on each side, one'r'elah'vely small
`and vertical to signify a pull, the other relatively large and horizontal to signify a
`push. Both has support the 'affordance of grasping: size and position specify
`whether the grasp is used to push or pull—though ambiguously.
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`Something that happens right after an action appears to be caused by
`that action. Touch a computer terminal just when it fails, and you are
`apt to believe that you caused the failure, even though the failure and
`your action were related only by coincidence. Such false causality is the
`basis for much superstition. Many of the peculiar behaviors of people
`using computer systems or complex household appliances result from
`such false coincidences. When an action has no apparent result, you
`may conclude that the action was ineffective. So you repeat it. In earlier
`days, when computer word processors did not always show the results
`of their operations, people would sometimes attempt to change their
`manuscript, but the lack of visible eEect from each action would make
`them think that their commands had not been executed, so they would
`repeat the commands, sometimes over and over, to their later astonish-
`ment and regret. It is a poor design that allows either kind of false
`causality to occur.-
`
`' TWENTY THOUSAND EVERYDAY THINGS
`
`There are an amazing number of everyday things, perhaps twenty
`thousand of them. Are there really that many? Start by looking about
`you. There are light fixtures, bulbs, and sockets; wall plates and screws;
`clocks, watches, and watchbands. There are writing devices (I count
`twelve in front of me, each different in function, color, or style). There
`are clothes, with different functions, openings, and flaps. Notice the
`variety of materials and pieces. Notice the variety of fasteners—but-
`tons, zippers, snaps, laces. Look at all the furniture and food utensils:
`all those details, each serving some function for manufacturability,
`usage, or appearance. Consider the work area: paper clips, scissors, pads
`of paper, magazines, books, bookmarks. In the room I’m working in,
`I counted more than a hundred specialized objects before I tired. Each
`is simple, brat each requires its own method of operation, each has to
`be learned, each does its own specialized task, and each has to be
`designed separately. Furthermore, many of the objects are made of
`many parts. A desk stapler has sixteen parts, a household iron fifteen,
`the simple bathtub-shower combination twenty-three. You can’t be-
`lieve these simple objects have so many parts? Here are the eleven basic
`parts to a sink: drain, flange (around the drain), pop-up stopper, basin,
`soap dish, overflow vent,spout, lift rod, fittings, hot-water handle, and
`cold-water handle. We can count even more if we start taking the
`faucets, fittings, and lift rods apart.
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`
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`1.6‘ When Affordances Fail. l had to tie a string around my cabinet door to afford
`pulling.
`‘ “ ‘
`l'?
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`Apple Inc.
`Exhibit 1016
`Page 009
`
`

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`The book What's What: A Visual Glossary of the Physical World has more
`than fifteen hundred drawings and pictures and illustrates twenty—
`three thousand items or parts of items.4 Irving Biederman, a psycholo-
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`gist who studies visual perception, estimates that there are probably
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`"30,000 readily discriminable objects for the adult.”5 Whatever the
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`exact number, it is clear that the difficulties of everyday life are ampli-
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`fied by the sheer profusion of items. Suppose that each everyday thing
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`takes only one minute to learn; learning 20,000 of them occupies
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`20,000 minutes—333 hours or about 8 forty-hour work weeks. Fur;
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`thermore, we often encounter new objects unexpectedly, when we are
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`really concerned with something else. We are confused and distracted,
`and what ought to be a siniple, effortless, everyday thing interferes
`with the important task of the moment.
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`How do people cope? Part of the «answer lies in the way the mind
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`works—in the psychology of human thought and cognition. Part lies
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`in the information available from the appearance of the objects——the
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`psychology of everyday things. And part comes from the ability of the
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`designer to make the operation clear, to project a good image of the
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`operation, and to take advantage of other things people might be ex-
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`pected to know. Here is where the designer’s knowledge of the psy-
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`chology of people coupled with knowledge of how things work
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`becomes crucial.
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`CONCEPTUAL MODELS
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`1.7 Carelman's Tandem "Convergent Bicycle (Model for Fiancés).” Jacques
`Carelman: ”Convergent Bicycle” Copyright © 1969—76—80 by Jacques Carelman
`and A. D. A. G. P. Paris. From Jacques Carelman, Catalog of Unfindable Objects, Balland,
`éditeur, Paris—France. Used by permission of the artist.
`
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`the scissors still work. You can figure out the scissors because their
`operating parts are visible and the implications clear. The conceptual
`model is made obvious, and there is effective use of affordances and
`constraints.
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`As a counterexample, consider the digital watch, one with two to
`four push buttons on the front or side. What are those push buttons
`for? How would you set the time? There is no way to tell—no evident
`relationship between the operating controls and the functions, no con-
`straints, no apparent mappings. With the scissors, moving the handle
`makes the blades move. The watch and the Leitz slide projector provide
`no visible relationship between the buttons and the possible actions,
`no discernible relationship between the actions and the end result.
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`Consider the rather strange bicycle illustrated in figure 1.7. You know
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`it won't work because you form a conceptual model of the device and
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`mentally simulate its operation. You can do the simulation because the
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`parts are visible and the implications clear.
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`Other clues to how things work come from their visible structure-—
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`in particular from aflordanres, ranstraints, and mappings. Consider a pair of
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`scissors: even if you have never seen or used them before, you can see
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`that the number of possible actions is limited. The holes are clearly
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`there to put something into, and the only logical things that will fit are
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`fingers. The holes are affordances: they allow the the fingers to be
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`inserted. The sizes of the holes provide constraints to limit the possible
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`fingers: the big hole suggests several fingers, the small hole only one.
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`The mapping between holes and fingers——the set of possible opera-
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`tions—is suggested and constrained by the holes. Moreover, the opera-
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`tion is not sensitive to finger placement: if you use the wrong fingers,
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`Principles of Design
`for Understandability and Usability
`
`We have now encountered the fundamental principles of designing
`for people: (1) provide a good conceptual model and (2) make things
`visible.
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`PROVIDE A GOOD CONCEPTUAL MODEL
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`A good conceptual model allows us to predict the effects of our actions.
`Without a good model we operate by rote, blindly; we do operations
`as we were told to do them; we can’t fully appreciate why, what effects
`to expect, or what to do if things go wrong. As long as things work
`properly, we can manage. When things go wrong, however, or when
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`Apple Inc.
`Exhibit 1016
`Page 010
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`we come upon a novel situation, then we need a deeper understanding,
`a good model.
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`For everyday things, conceptual models need not be very complex.
`After all, scissors, pens, and light switches are pretty simple devices.
`There is no need to understand the underlying physics or chemistry of
`each device we own, simply the relationship between the controls and
`the outcomes. When the model presented to us is inadequate or wrong
`(or, worse, nonexistent), we can have difficulties. Let me tell you about
`my refrigerator.
`
`My house has an ordinary, two—compartment refiigerator—notlung
`very fancy about it. The problem is that I can’t set the temperature
`properly. There are only two things to do: adjust the temperature of the
`freezer compartment and adjust the temperature of the fresh food
`compartment. And there are two controls, one labeled ”freezer, ” the
`other d’fiesh food. ” PVhat’s the problem?
`,
`You try it. Figure 1.8 shows the instruction plate from inside the
`refuge-Ia tor. Now, suppose the freezer is too cold, the fresh food section
`just right. You want to make the freezer warmer, keeping the fresh food
`constant. Go on, read the instructions, figure them out.
`
`1.8 My Refrigerator. Two compartments—fresh food and freezer—and two con—
`trols (in the fresh food unit). The illustration shows the controls and instruct-ions.
`Your task: Suppose the freezer is too cold, the fresh food section just right. How
`would you adjust the controls so as to make the freezer warmer and keep the fresh
`food the same? (From Norman, 1986.)
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`NORMAL SETTINGS
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`COLDER FRESH FOOD
`GOLDEST FRESH FOOD
`COLDER FREEZER
`WARMEH FRESH FOOD
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`1 SET BOTH CONTROLS
`2 ALLOW 24 HOURS
`To STABILIZE
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`8-7
`8-9
`7-8
`4-1
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`COOLING UNIT
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`COLD AIR
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`FRESH
`FOOD
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`FRESH FOOD
`CONTROL
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`COOLING UNIT
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`Thermostat i
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`COLD AlFl
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`1.9 Two Conceptual Models for My Refrigerator. The model A (above) is
`provided by the system image of the refrigerator as gleaned from the controls and
`instructions; B (below) is the correct conceptual model. The problem is that it is
`impossible to tell in which compartment the thermostat is located and whether the
`two controls are in the freezer and fresh food compartment, or vice versa.
`Thermostat
`
`(location
`not known)
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`CONTROL A
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`COOLING UNIT
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`OFF (FRESH FD & FRZ)
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`O
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`FRESH FOOD
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`ABCDE
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`sneezea
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`76543
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`Apple Inc.
`Exhibit 1016
`Page 011
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`Perhaps the designers thought the correct model was too complex, that
`the model they were giving was easier to understand. But with the
`wrong conceptual model, it is impossible to set the controls. And even
`though I am convinced I now know the correct model, I still cannot
`accurately adjust the temperatures because the refrigerator design
`makes it impossible for me to discover which control is for the thermo-
`stat, which control is for the relative proportion of cold air, and in
`which compartment the thermostat is located. The lack of immediate
`feedback for the actions does not help: with a delay of twenty-four
`hours, who can remember what was tried?
`
`The topic of conceptual models will reappear in the book. They are
`part of an important concept in design: mental models, the models people
`have of themselves, others, the environment, and the things ‘with
`which they interact. People form mental models through experience,
`training, and instruction. The mental model of a device is formed
`largely by interpreting its perceived actions and its visible structure. I
`call the visible part of the device the system image (figure 1.10). When
`the system image is incoherent or inappropriate, as in the case of the
`refrigerator, then the user cannot easily use the device. If it is incom-
`plete or contradictory, there willbe trouble.
`
`MAKE THINGS VISIBLE
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`Oh, perhaps [’11 better warn you. The two controls are not indepen-
`dent. The freezer control ah‘ects the fresh food temperature, and the
`fresh food control ahfects the freezer: And don ’t forget to wait twenty-
`four hours to check on whether you made the right adjustment, ifyou
`can remember what you did.
`
`Control of the refrigerator is made difficult because the manufac—
`turer provides a false conceptual model. There are two compartments
`and two controls. The setup clearly and unambiguously provides a
`simple model fOr the user: each control is responsible for the tempera-
`ture of the compartment that carries its name. Wrong. In fact, there is
`only one thermostat and only one cooling mechanism. One control
`adjusts the thermostat setting, the other the relative proportion of cold
`air sent to each of the two compartments of the refrigerator. This is
`why the two controls interact. With the conceptual model provided by
`the manufacturer, adjusting the temperatures is almost impossible and
`alWays fr