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Bernard J. Jansen

I n t r o d u c t i o nThere are a variety of uni-versity-level hum an- com -puter interaction (HCI)programs. Although a fewoffer breath and diversity,many students graduatefrom universities that offeronly one or two CH Icourses. As such, most stu-

4,..,a dents have a limi ted back-grou nd in the various CH Iareas. This article offers ageneral overview in onearea, graphical user inter-faces (GUI ). A GU I allowsa computer user to movefrom application to appli-cation. A good GU Imakes an application easy,practical, and efficient touse, and the marketplacesuccess o f today's softwareprograms depends ongood GUI design. Con-sider the Macintos h andthe IBM-PC. Computer users view

Apple's Macintosh co mputers as havingthe best GUI. Correspondingly, theirpositive view of the Macintosh system isalmost double that of the Windowsusers. Correspondingly, brand loyaltyamo ng Macinto sh users is almost 20%higher than that for Wind ows users. Thedevelopment of new software isextremely expense. Wi th success or fail-ure of a product an d ma ybe the entirecom pan y depende nt on the application'sGUI reception in the marketplace, agood G UI design is extremely important.Unfortunately, it is not easy to define ifan application's GUI is easy, practical, orefficient. These are attributes t hat do n otlend themselves to counting. T he mar-ketplace does attem pt to access theseattributes, however (Bonsiepe 1993), buteven after over 10 years of GUI develop-ment, there are still questions conce rni ngwhat is a good GU I design. For example,the early Macin tosh Apple used the Trashcan icon as a meta pho r for deleti ng files.However, one can pull items out of a

The G raph ical U se r InterfaceAn Inlroduclio

trashcan until the trash person comes.Th e first trash can icon did no t allow thisretrieval. This contextual inc ongr uitycaused users many problems. As anotherexample, the Windows 95 GUI is themost modern of all GUIs. One wouldexpect it to be fairly well developed an drelatively error free. However, o f theapproximately 90 complaints with Win-dows 95, no ne are performance com-plaints. They are all human factors typecomplaints, such as how to copy a fileand ho w to get rid of annoying icons(An ony mou s 1995). Finally, people haveso many complaints about the X-Win-dowing System, the third major G UIstandard, that there is whole boo k aboutwhat is wron g with it (Hopkins 1996).This paper will survey the co mm on defi-nitions of what a GUI is and review thethree common GUI standards in themarke t today. It will then review three ofthe many h uman factor concepts under-lying good GUI design, which are visualacuity, limits to absolute memory, andthe principle of grouping. The paper willthen present the effect of these factors onthree GUI design areas, the amount ofpresented information, the grouping ofinformation, and the placement of thisinfo rmat ion on the screen. Following thissection, the ramifications of bad versusgood G UI design will be addressed. Areasfor research and likely directions o f futureGU I design conclude the paper.G U l sAlthough there are numerous GUIs inthe market today, the exact definition ofa GU I is still fuzzy. This ma y be due tothe fact that GUIs are relatively new.There are three deJhctaGUI-standardsthat are the basis for all GUIs. Th is sec-tion reviews the com mo n definition ofGUIs, the history of GU I development,and G UI standards in the marketplace.D e f i n i t i o nA GUI is a type of computer humaninterface on a comp uter. It solves theblank screen problem that confrontedearly compu ter users (Nor man 1988).

These early users sat down in front of acomp uter and faced a blank screen, witonly a prompt. The computer gave theuser no indication what the user was todo next. GU Is are an attem pt to solve thblank screen problem. At a conceptuallevel, a computer human interface is a"means by which people and computercommunicate with each other" ( Norma1988). One can make an analogybetween a computer system's GUI and car's steering wheel. T he wheel directlybinds the driver to the operation andfunctionality of the vehicle. When driving, a driver should not have to concentrate on the steering wheel. In the sameway, the GUI binds the user of the computer system to the operation an d potential of the c omput er system (Bonsiepe1993). A good G UI design removes thimpediment of communication with thcomputer system and allows the user towork direcdy on the problem at hand(Norman 1988). In computer scienceterms, the GUI is a visual operating display that the monit or presents on themonitor to the computer operator (Hading 1989). More specifically, a GUI is specification for the loo k and feel of thecomp uter system (Bonsiepe 1993). GUIusually have c om mo n characteristic sucas windows, icons, menus, and pointers(WI MP) . Collectively, WIM Ps are pic-tures that bring forth a certain action oan action space. The user issues com-mands via the GUI to computer applictions. GUIs usually have three majorcomponents. These three componentsare (Hayes and Barab 1989): a windowing system, an imaging model, and anapplication program interface (API). Thwindow ing system builds the windows,menus, and dialog boxes that appear onthe screen. The imaging model definesthe fonts and graphics that appear on thscreen. WIMP s are products of both thwindow ing system and imaging model.Finally, the API is the means in which thuser specifies how an d what w indow s angraphics appear on the screen. The his-torical developme nt of the GU I stillimpacts the three major GUI paradigmin the marke t today. Historically, all

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m o d e r n G U I s a r e o f f sh o o ts o f t h e A p p l eM a c in to s h . T h i s h a s l e a d to a g re a t d ea lo f s t a n d a r d i z at i o n a n d c o n s i s te n c ya m o n g G U I d e s i g n c ri t er i a. T h e r e f o r e ,m o s t a p p l ic a t i o n s' G U I s a d h e r e t o o n e o ft h e t h r e e m a j o r G U I p a r a d i g m s , t h eA p p l e M a c i n t o s h , t h e I B M S y s t e m sA p p l i c a t io n A rc h i t e c tu re (S A A ) , o r t h eX - W i n d o w i n g S y s te m . W h i l e n o n e o fth e s e G U I d e s ig n s are p e r fe c t , t h e o v e ral ld e s ig n c o n c e p t s a re g o o d e n o u g h t om a k e r a d ic a l d e p a rt u r e s c o u n t e r p r o d u c -t iv e (N o rm a n 1 9 8 8 ) , u n le s s th e re a re s ig -n i f i ca n t p e r f o r m a n c e e n h a n c e m e n t s .H i s t o r yR e s e a rc h e r s a t t h e X e ro x P a lo A l toR e s e a rc h C e n te r d e s ig n e d th e f i r s t a p p l i -c a t io n w i th a G U I , t h e X e ro x S ta r , i n1 9 7 7 . T h e X e r o x S t ar w a s u n i q u eb e c a u s e th e r e s e a rch e r s c a re fu l ly d e s ig n e dt h e c o m p u t e r h u m a n i n t e r f a c e b e f o r et h e y b e g a n d e s i g n i n g t h e i n t e r n a l w o r k -in g s o f t h e a p p l i c a t io n . U n fo r tu n a te ly ,th e X e ro x S ta r w a s to o s lo w , a n d i t w a sn o t c o m m e rc ia l ly s u c c es s fu l. H o w e v e r ,S te v e J o b s v i s i t e d th e P a lo A l to R e s e a rc hC e n t e r a n d s a w X e r o x S ta r. H e r e t u r n e dt o A p p le C o m p u t e r a n d s u b s e q u e n tl yh i re d s e v e ra l o f t h e o r ig in a l d e s ig n e r s o fX e ro x S tar . T h e y f i r s t p ro d u c e d th eA p p le L i s a. L ik e th e X e ro x S ta r , t h eA p p l e L i sa w a s n o t c o m m e r c i a l l y su c ce s s-fu l . In 1 9 8 4 , t h e y d e v e lo p e d th e c o m -m e rc ia l ly su c c e s sfu l A p p le Ma c in to s h . Int h e b r o a d e s t t e r m s , th e M a c i n t o s h 's G U Id e f i n e d t h e l o o k a n d f e el o f a ll G U I stoday .D e F a c t o S t a n d a r d sT h e A p p l e M a c i n to s h , t h e I B M S AA ,a n d X - W i n d o w i n g S y s te m a r e t h e p a ra -d i g m s f o r al l m o d e r n G U I s . B e c a u se o fth e i r i n f lu e n c e in th e s t a n d a rd iz a t io n o ft o d a y 's G U I d e s ig n , a b r i e f d e s cr i p t i o n o fth e m a jo r f e a tu re s o f e a c h s t a n d a rd i snecessary.A p p l e M a c i n t o s hA p p l e i n t r o d u c e d t h e M a c i n t o s h a s ac o m p u t e r " f o r r e st o f u s ." T h e G U I w a s am a j o r p a r t o f t h e o v e r al l g o a l o f th e M a c -in to s h . A l l g ra p h ic a l a p p l i c a t io n s c o p ie dth e Ma c in to s h in i t s d e s ig n a n d u s a g e .T h e M a c i n t o s h i n t r o d u c e d t h e f i r s tm e n u , i c o n s , a n d p o i n t - a n d - c l i c k , m o u s ed r i v e n p r o ce s s in g . W i t h t h e se m e n u s a n dic o n s , t h e Ma c in to s h w a s th e f i r s t com-

p u te r s y s t e m th a t l im i t e d th e u s e r s t oc o n te x tu a l ly c o r re c t a n s w e rs . F o r e x a m -p le , o n c e th e u s e r m a d e a s e l e c t io n v i a am e n u , t h e m e n u l i m i t e d t h e u s e r' s s u b se -q u e n t a c t io n s . T h e u s e r c o u l d n o l o n g e rc h o o s e s o m e t h i n g m e a n i ng l e s s. T h eM a c i n t o s h ' s G U I h a s a ll t h r e e m a j o rc o m p o n e n t s o f a G U I , w h i c h ar e t h ew i n d o w i n g s y s t e m , a n i m a g i n g m o d e l ,a n d a n A P I .I B M S A AU n l i k e t h e A p p l e M a c i n t o s h , t h e I B M -S A A is m o r e t h a n j u s t a G U I . I t is aw h o l e s y s t e m o f i n t e rf a c es t h a t c a n s p a nm a c h i n e s f r o m p e r s o n a l t o m a i n f r a m ec o m p u t e r s . A s s u c h , i t i nc l u d es m a n yf u n c t i o n s t h a t m o s t G U I s d o n o t , i n c l u d -i n g a s u it e o f n e t w o r k i n g a n d d a t a b a s et o o ls . T h e S A A 'S G U I p o r t i o n h a s a llt h re e G U I c o m p o n e n t s . A n o t h e r u n i q u ei t e m o f th e S A A is t h a t t h e u s e r d o e s n o tn e e d a m o u s e t o i n t e r a c t w i t h t h e a p p l i -c a t io n . A l l a c tio n s c a n b e e x e c u te d f ro mth e k e y b o a rd , fu n c t io n a l i t y n o t a v a i l a b lei n t h e M a c i n t o sh G U I . T h e m o s t c o m -m o n S A A - t y pe G U I s a re W i n d o w s 3 .1 1f o r D O S a n d t h e P r o g r a m M a n g e r f o rO S / 2 .M I T X - W i n d o w s S y s te mA l t h o u g h a s e p a r at e G U I s t a n d a r d , m a n yX - W i n d o w b a s ed G U I s , s u c h as M o t i fa n d T C L / T K , h a v e c o p i e d th e l o o k a n df ee l o f t h e I B M S A A . X - W i n d o w s i s s ti llt h e u n d e r l y i n g l i b r a r y f o r t he s e G U I s .T h e X - W i n d o w i n g S y s te m is th e m o s tp o p u l a r G U I f o r U N I X s y st em s . T h i s i sb e c a u se a n y X - W i n d o w s s o f t w a r e ca n u s et h e X - W i n d o w s l ib r ar y , w h i c h g i ve s i tg re a t p o r t a b i l i t y a n d s t a n d a rd iz a t io na c ro s s p l a t fo rm s .X - W i n d o w s a l s o w o r k s d i r e c t ly w i t h n e t -w o r k s , w h i c h a l l o w s t h e G U I d i s p la y t ob e o n o n e c o m p u t e r a n d t h e a p p l ic a t i o nt h a t t h e u s e r n ee d s o n a n o t h e r c o m p u t e r .I t d oe s n o t m a t t e r i f t he t w o c o m p u t e r sa re in d i f f e re n t ro o m s o r o n d i f f e re n tc o n t i n e n t s . I t a d d i ti o n t o t h e t h r e e c o m -m o n G U I c o m p o n e n t s , X - W i n d o w s h a sa c o l l ec t o f a p p l i c a t io n to o l s a n d u t i l it i e sa s a b u i l t i n X -L ib ra ry .T h e o r e t i c a l B a c k g r o u n dA l t h o u g h G U I s a r e an i n t e g ra l p a r t o f a na p p l i c at i o n , G U I s a r e n o t i n h e r e n t l y e a s -i e r t o u s e t h a n c o m m a n d l i ne i n t er f ac e s .

T h e q u a l i t y o f t h e d e s ig n i s th e o v e r r i d -in g i s s u e fo r a l l i n t er f a c e s (B e n b a s a t a n dT o d d 1 9 9 3 ; B e t t s 1 9 9 5 ) . T h e re a re s e v -e ra l s c re e n d e s ig n g u id el in e s . O n th eo t h e r h a n d , t h e r e i s s h o r t a g e o f e m p i r i c a ls tu d ie s s u b s t a n t i a t in g th e s e g u id e lin e s .T h i s l a c k o f e m p i r i c a l r e s e a rc h is e sp e -c i al l y a p p a r e n t f o r m o d e r n G U I d e s i g n s,s u c h as W i n d o w s 9 5 , Q u i c k e n 7 . 0 , a n dD b a s e 5 . In a n a r ro w e r s e n s e , t h e re a ree m p i r i c a l s tu d ie s th a t h a v e id e n t i f i e db a s i c p s y c h o lo g ic a l f a cto r s t h a t o n es h o u l d c o n s i d e r i n t h e d e s ig n o f g o o dG U I s . T h i s p a p e r w i ll n a r r o w t h e d i s c u s-s i o n to t h r e e p r i m a r y c o n t r i b u t i n gh u m a n f a c to r s , w h i c h a re : T h e p h y s ic a l l im i t s o f v is u a l a cu i ty . T h e l i m i t s o f a b so l u t e m e m o r y . T h e G e s ta l t P r in c ip l e .Visual A cuityV is u a l a c u i ty i s t h e a b i l i t y o f t h e e y e tore s o lv e d eta i l. T h e r e t in a o f e y e c a n o n lyf o c us o n a v e ry s m a ll p o r t i o n o f a c o m -p u t e r s c r e e n , o r a n y t h i n g f o r t h a t m a t t e r ,a t a n y o n e t i m e ( W i c k e n s 1 9 9 2 ) . T h i s isb e c a u s e , a t a d i s t a n c e g re a t e r t h a n 2 . 5d e g re e s f ro m th e p o in t o f f i x a tio n , v i su a la c u i ty d e c re a s e s b y h a lf . T h e re fo r e , a c i r -c l e o f r a d iu s 2 .5 d e g re e s a ro u n d th e p o in to f f ixa t ion is wh a t the use r can see c lea r ly .I n t h e G U I w o r l d , t h i s is t h e R u l e o f 1 . 7( S a r n a 1 9 9 4 ) . A t a n o r m a l v i e w i n g d i s-tance o f 19 inches , 5 degrees t rans la tesin to a b o u t 1 . 7 in c h e s . A s s u m in g a s t a n -d a rd s c re e n fo rm a t , 1 . 7 in ch e s i s a n a re aa b o u t 1 4 c h a r a c te r s w i d e a n d a b o u t 7l in e s h ig h (H e la n d e r 1 9 8 8 ) . T h i s i s t h ea m o u n t o f i n fo r m a t i o n t h a t a u s e r ca nt a k e i n a t a n y o n e t i m e , a n d i t l im i t s t h ee ffec t ive s ize o f icons , menus , d ia logsb o x e s , e t c . I f u s e r s m u s t c o n s t a n t ly m o v ethe ir eyes ac ross the sc reen to c lea r lyfo c u s , t h e G U I d e s ig n i s c a u s in g a lo t o fu n n e c e s s a ry a n d t i r in g e y e m o v e m e n t .Information LimitsO n c e th e u s e r h a s a d e s i r e d f ix a t io np o i n t , t h e r e i s a l i m i t to t h e a m o u n t o fi n f o r m a t i o n t h a t t h e p e r s o n c a n p ro c e s sa t o n e ti m e . A G U I d e s i g n r u le o f t h u m bis th a t t h e r a n g e o f o p t io n s o r c h o ic e ss h o u l d n e v e r b e m o r e t h a n f iv e o r s i x(Mi l l e r 1 9 5 6 ; S a rn a 1 9 9 4 ) . S e m in a l w o rkb y M i l l e r i s t h e b a s i s fo r t h i s ru l e . Mi l l e r(Mi l l e r 1 9 5 6 ) s h o w e d th a t a b s o lu te id e n -t i f i c a t io n u s in g o n e -d im e n s io n a l c r i t e r i aw a s a b o u t s e v e n i t e m s , p l u s o r m i n u st w o . H e s h o w e d t h a t t h is l i m i t a t i o n a l soh e l d f o r m e m o r y s p a n . M i l l e r in t r o d u c e d

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t h e c o n c e p t o f r e c o d i n g a s a m e t h o d t h a tp e o p l e u s e to s t o r e i n f o r m a t i o n . M i l l e ra l so p o i n t e d o u t t h a t b y e x p a n d i n g t h ei d e n t i f i c a t i o n c r i t e r i a f r o m o n e t o m o r ed i m e n s i o n s p e o p l e c ou l d h a n d l e m o r ec h oi c es a n d r e m e m b e r m o r e . L a t e rr e s ea r c h e rs e x p a n d e d o n M i l l e r r e c o d i n gt o d e v e l o p th e c o n c e p t t h a t p e o p l e c h u c ki n f o r m a t i o n t o g e t h e r i n o rd e r t o r e m e m -b e r m o r e i n f o r m a t i o n ( B a d d el e y 1 9 9 4 ;S h i f f r in 1 9 9 4 ) . T h i s r e s ea r c h h as d i r e c ti m p a c t o n G U I d e s i gn , e s p ec i a ll y c o n -c e r ni n g t he n u m b e r o f m e n u i te m s a n dic o n s .G e s t a l t P r i n c i p leT h e G e s t a l t P r i n c i p l e st a te s t h a t p e o p l eu se a t o p - d o w n a p p r o a c h t o o r g a n i zi n gd a t a ( H e l a n d e r 1 9 8 8; W i c k e n s 1 9 9 2) .T h i s p r i n c i p l e c a n i n f l u e n c e h o w o n es h o u l d o r g a n i z e g r a p h i c a l i n f o r m a t i o no n t h e s cr e en . T h e G e s t a lt s c h oo l o f G U Id e s ig n e r s h a s a t t e m p t e d t o i d e n t i f y c r i te -r i a t h a t c a u s e p e o p l e t o g r o u p c e r t a i ni t e m s t o g e t h e r i n a d is p la y . P r o p e r g r o u p -i n g r e s u lt s i n a n e ce s s a r y r e d u n d a n c y o fs e l ec t i o n i n f o r m a t i o n t h a t a i d s t h e u se r .F o r e x a m p l e , i f u s er s k n o w w h e r e o n ei t e m in a g ro u p i s o n a s c re e n , t h e y w i l le x p e c t o t h e r l i k e i t e m s t o b e t h e r e a l so . I fo n e g r o u p s t h e i t e m s i n l i n e w i t h t h i se x p e c ta t io n , i t a l l o w s fo r a c c u ra t e lo c a t -i n g a n d b e t t e r t ra n s fe r o f i n f o r m a t i o n t ot h e u s e r . T h e t o p - d o w n a p p r o a c h a l s oa ll ow s f o r t h e d e v e l o p m e n t o f e m e r g e n tfe a tu re s . A n e m e rg e n t f e a tu re i s a g lo b a lp r o p e r t y o f a se t t h a t i s n o t e v i d e n t w h e no n e v i e w s e a c h i t e m lo c a l ly . S in c e g lo b a lp r o c e s s i n g t e n d s t o b e a u t o m a t i c , o n ec a n a r g u e t h a t a n e m e r g e d f e a t u r er e d u c e s th e a t t e n t i o n d e m a n d a s a u s ero p e r a t e s a m u l t i - e l e m e n t d i sp l ay . F o r t h i sp e r f o r m a n c e e n h a n c e m e n t , o n e m u s t u s eth e G e s ta l t P r in c ip l e in th e in i t i a l p l a c e -m e n t , a n d t h e r e s u l t i n g o r g a n i z a t i o nm u s t b e c o m p a t i b l e w i t h t h e u s e r 's c o g n i -t i ve v i e w o f t h e t a s k ( W i c k e n s 1 9 9 2 ) .G U I D e s i g n C o n s i d e r a t i o n sC o n s i d e r i n g t h e a b o v e p s y c h o l o g i ca l f ac -t o r s , o n e c o u l d c o m e t o t h e c o n c l u s i o nt h a t o n e c o u l d e a s il y e x t r a p o l a t e t h e sef a c t o rs t o t h e d e s i g n o f a g o o d G U I .E m p i r i c a l s t u di e s o f G U I s s h o w t h a t t h i sin tu i t i o n th i s i s n o t a lw a y s th e c a s e . T h eR u l e o f 1 . 7 d i r e c t l y le a d s t o t h e c o n c l u -s i o n t h a t a g o o d G U I w o u l d u s e a lo t o fi c o n s . U n f o r t u n a t e l y , t o o m a n y r a n -d o m l y p l a c e d i c o n s v io l a t e t h e l i m i t s o fa b s o lu t e m e m o r y . U s i n g t h e G e s t al t P r i n -

c i p le , o n e c a n g r o u p l i k e i t e m s t o g e t h e ru s i n g f a c t o r s l ik e c o lo r t o a d d m o r e i n f o r -m a t i o n a l d i m e n s i o n s . T o o m a n y c o l o rs ,h o w e v e r , d e s t r o y t h e g l o b a l v i su a l g r o u p -i n g o f t h e i t e m s . T h e u s e r t h e n b e g i n s t oc o n c e n t r a t e s o n t h e G U I . A n y p r i m a r yc o g n i t i v e t as k a t t e n t i o n d e v o t e d t o t h ei n t e r fa c e m a y i n t e r f e r e w i t h t h e p r i m a r yt a sk ( N o r m a n 1 9 8 8) . O n e c a n de r iv eb a si s G U I s t a nd a r d s f r o m b a s ic h u m a nf a c t o rs , h o w e v e r . T h e s e s t a n d a r d s a r e t h ep r e s e n ta t i o n o f in f o r m a t i o n , t h e g r o u p -i n g o f i n f o r m a t i o n , a n d i n f o r m a t i o ns e q u e n c i n g .A m o u n t o f I n fo r m a t io n P r e s e n t e dT h e a m o u n t o f i n f o r m a t i o n t o pr e s e n t ist h e m o s t b a s i c o f G U I d e s ig n c o n s i d e r-a t io n s . H . E . D u n s m o r e ( H e l a n d e r 1 9 88 ;R e i t e r er 1 9 9 3 ) s h o w e d t h a t m a k i n gs c r ee n s l es s c r o w d e d i m p r o v e s s c r e e nc l a r i ty a n d r e a d ab i l it y . A s s u ch , G U Id e s ig n e r s u s u a l ly fo l lo w th e g u id a n c et h a t t h e i n t e r fa c e s h o u l d d i s p l a y o n l yw h a t t h e u s e r n e e d s t o p e r f o r m t h e c u r -r e n t o p e r a t i o n . E m p i r i c a l r e s e ar c h e r ss h o w t h a t l i m i t i n g t h e i n f o r m a t i o n t oth a t n e c e s s a ry fo r t h e u s e r r e d u c e s e r ro r sa n d t i m e t o p e r f o r m t a s k s . E r r o r s a n dp e r f o r m a n c e t i m e i n c r ea s e a s th e G U Ip r e se n t s m o r e i n f o r m a t i o n . O f c o u r se , i tr e q u i re s a t h o r o u g h a n a l y si s o f t h e t a s k st h a t t h e u s e r m u s t p e r f o r m i n o r d e r t od i s p l a y o n l y t h e n e c e s s ar y a m o u n t o fi n f o rm a t i o n . C o m p a r e d t o a r a n d o m l yp la c e d s c re e n , a w e l l -d e s ig n e d s c re e n c a nr e d u c e t i m e n e e d e d t o p e r f o r m a t as k b ya s m u c h a s 4 0 % ( H e l a n d e r 1 9 8 8; L i na n d D a l y 1 9 9 4 ) . W a y s t o c o n s e r v e s c r e ens p a c e a re :1 . A p p r o p r i a t e u s e o f a b b r e v i a t io n s :M a n y d e si gn d o c u m e n t s r e c o m m e n d

u s i n g c o m p l e t e w o r d s w h e n e v e r p o ss i-b l e . D u e to s c re e n s i z in g c o n s t r a in t s , i ti s n o t a l w a y s p o ss i b l e t o u s e c o m p l e t ew o r d s . W h e n c o m p l e t e w o r d s a re n o tp o s s ib l e , a b b r e v i a t i o n s s h o u l d b e c o n -t e x t u a l a n d c o n s i s te n t . A g o o d c o n t e x -tu a l e x a m p le i s " h , " w h ic h i s u s u a l ly ag o o d a b b r e v i a t i o n t o u s e f o r he l p . T h en u m b e r o f a b b r e v ia t i o n s s h o u l d n o to n l y b e c o n t e x t u a l b u t a l s o b e k e e p t oa m i n i m u m . A s a p o o r e x a m p l e , i n th eU N I X s y st e m , th e " ls " c o m m a n d l is tf il es i n a d i r ec t o r y . T h e " I s" c o m m a n dh a s t 7 d i f f e re n t o n e - l e t t e r a b b re v ia -t i o n s t h a t c h a n g e t h e o u t p u t o p t i o n s o ft h e " Is " c o m m a n d . T h e o n e - l e t t era b b r e v i a t i o n s h a v e l i t t l e c o n t e x t u a ll i n k t o t h e o p t i o n s t h e y r e p r e s e n t. I n

f ac t, t h e U N I X s y s t em i s a g o o d e x a mp l e o f w h a t n o t t o d o .

2 . A v o i d u n n e c e s s a r y d e ta i l: F o r e x a m p l eu s e w h o l e n u m b e r s i f o n e d o e s n o tn e e d d e c im a l s . K e e p t h e w i n d o w a n di c o n d e s i g n s c l e ar a n d s i m p l e . E v e nw h e n u s er s p r e f e r m o r e c o m p l e x i c o n se l a b o r a t e i c o n s a d d n o t h i n g t o p e r f o rm a n c e . S t u d i e s s h o w t h a t w h e n i c o nd e s i g n s a r e t o o c o m p l e x , t i m e t o c o mp le t e a t a s k a c tu a l ly in c re a s e s (B e n b a s aa n d T o d d 1 9 9 3) . I n s t u di e s w i t h 3 - Da n d 2 - D g r a p h i c a l d i sp l a y s, u s er s p r e -f e r r e d t h e 3 - D d i sp l a y s. T h e r e w e r e n od i f f e r e n c e s i n p e r f o r m a n c e b e t w e e nt h e t w o g r a p h i c a l d i s p la y s , h o w e v e r( H u b o n a 1 9 9 5 ) .

3 . U s e c o n c is e w o r d i n g : S c r e e n s h a v el im i t e d s p a c e . S c re e n d e s ig n e r s s h o u lda v o i d t h e t e n d e n c y t o p l a c e a d d i t i o n ad a t a o n t h e s c r e e n j u s t b e c a u s e t h e d a t ai s a v a i l a b le . Mo re o b je c t iv e l im i t s o fs c r ee n d e n s i t y v a r y f r o m t h r e s h o l d s o2 5 % t o 8 0 % ( H e l a n d e r 1 9 8 8 ) . T h e r ei s n o e m p i r i c a l r e s e a r c h t h a t s u b s t a n t ia te s a n y p e r f o r m a n c e e n h a n c e m e n tw i t h a n y s p e c i fi c t h r e sh o l d .

4 . U s e f a m i l i ar d a ta f o r m a t s : W i t h m o r efa m i l i a r fo rm a t s , t h e u s e r w i l l n e e d l esi n f o r m a t i o n t o c o m p l e t e t h e t as k . A ne x a m p l e f o r d a t a e n t r y i s t h e s t a n d a r dU S A a d d r e s s f o r m a t o f s t r e et , c i ty ,s t a t e , a n d z ip c o d e . In a d d i t io n a l t ore q u i r in g l e ss i n s t ru c t io n , t h e u s e r w i lp e r f o r m t h e o p e r a t i o n f a st e r t h a n i f t h ef o r m a t i s u n f a m i l i a r .5 . U s e t a b u l a r f o r m a t s w i t h c o l u m nh e a d i n g s: T a b u l a r f o r m a t s a l l o w fo re f f i c i e n t l a b e l in g o f r e l a t e d d a ta . I t i se s p e c ia l ly p re fe ra b le fo r d a t a lo c a t io nt a sk s . S i m p l y s p l i t t i n g i t e m s o n o n el o n g l i n e i n t o a t w o - l i n e r e s u l t i n p r od u c ti v i ty i m p r o v e m e n t s o f 2 0 %( S a r n a 1 9 9 4 ) . A l so , L a L o m i a a n dC o o v e r t ' s r e s ea r c h ( H e i a n d e r 1 9 8 8 )s h o w e d t h a t l o c a t i n g a d a t a v a l u e w a sq u i c k e r i n t a b u l a r f o r m t h e n i n a r a nd o m o r g ra p h f o r m a t . F o r t r e n d a n a lys i s , a l i n e g ra p h i s q u ic k e r t h a n r a wd a t a ( H e l a n d e r 1 9 8 8) .

G r o u p i n g o f I n fo r m a t io nG i v e n a se t o f i n f o r m a t i o n t o d i s pl a y,t h e r e a r e m a n y w a y s o n e c a n d i s p l a y t h ei n f o r m a t i o n . P r o p e r g r o u p i n g i m p r o v e st h e i n f o r m a t i o n ' s r e ad a b i l i t y a n d c a nh i g h l i g h t r e l a t i o n s h i p s b e t w e e n t h ei n f o r m a t i o n ( H e l a n d e r 1 9 8 8 ) . T u l l i s '( H e l a n d e r 1 9 8 8 ) ( S a r n a 1 9 9 4 ) e x p e r i -m e n t s i n t h e m i d - 1 9 8 0 s s h o w e d t h a t t h

24 Ap r il 199 8 Vo lum e 0 , Num ber 2 S IGCH I Bu llet in

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b e s t p r e d i c t o r s o f s e ar c h t i m e w e r e t h en u m b e r o f a n d s i ze o f t h e g r o u p s. T h e r e -f o r e , o n e s h o u l d s t r u c t u r e d i s p l a y s w i t ht h e l i m i t s o f v i s u a l a c u i t y i n m i n d . T h e.use r needs to be ab le to t ake in the d i f fe r -e n t c h u n k s o f in f o r m a t i o n a t o n e g l an c et o i m p r o v e r e a d a b i l i t y . O v e r a l l , t h e b e s tp r e d i c t o r s o f e as e o f u s e w e r e d e n s i t y a n di t e m a l i g n m e n t . E m p i r i c a l r e s e a r c hs h o w s t h a t s e a r c h t i m e i n c r e a s e s a s t h es i ze o f t h e g r o u p i n g e x c e e d s 5 d e g r ee s o fa r c a n d t h e n u m b e r o f g r o u p i n g si n c r ea s e s a b o v e f i v e ( H e l a n d e r1 9 8 8 ) ( W i c k e n s 1 9 9 2 ). W i t h g r o u p i n g sless than 5 degrees , the sea rch dura t io n i sd i r ec t ly a f u n c t i o n o f t h e t o t al n u m b e r o fg r o u p i n g s o n t h e s c r e e n ( H e l a n d e r1 9 8 8 ) . T h e r e a r e s e v e ra l t e c h n i q u e s t oa i d i n t h e g r o u p i n g o f i n fo r m a t i o n ,w h i c h i n c l u d e :1 . C o l o r : P r e s e n t i n g d i f f e r e n t g r o u p s

w i t h d i f f e r e n t c o l o r c l e a r l y c r ea t e ss o m e d e g r e e o f g r o u p i n g a m o n g t h ee l e m e n t s o f t h e s a m e c o lo r . G U I s t h a tu t i l i ze co lo r we l l inc rease p roduc t iv i ty .I f l i k e c o l o r i t e m s a r e i n c l o s e p r o x i m -i ty , the v i sua l a s soc ia t ion i s s t rongert h a n i f t h e l i k e c o l o r i t e m s a r e f u r t h e ra p a r t . I n a d d i t i o n t o c h a n g i n g t h ei t em ' s co lo r s , one can use d i f fe ren t co l -o r s f o r t h e b a c k g r o u n d a n d f o r e -g r o u n d . T h e e f f e c t i v e n es s o f t h i st e c h n i q u e d e c r e as e s a s t h e n u m b e r o fs c r e e n c o l o r s in c r e a se s ( H e l a n d e r1 9 8 8 ) . O v e r u s e o f c o l o r d e g r a d e s p e r -f o r m a n c e , h o w e v e r .

2 . G r a p h i c a l B o u n d a ri e s : D r a w i n gb o u n d a r i e s a r o u n d e l e m e n t s i s t h em o s t c o m m o n m e t h o d o f g r o up i n ge l e m e n t s in G U I s . A l t h o u g h t h e r e isn o e m p i r i c a l e v i d e n c e t o s h o w t h a tt h e se g r o u p i n g s i m p r o v e p e r f o r m a n c e ,u s e rs p r e f e r t h i s t y p e o f g r o u p i n g sc o m p a r e d t o o t h e r m e t h o d s . T h i st e c h n i q u e i s e s p e c i al l y p o p u l a r w i t ht h e I B M S A A sy s te m s . A n o t h e rm e t h o d o f g r o u p i n g i s t o g r o u p t a s k sw i t h i n i c o n s . I c o n g r o u p i n g i s e a s yb e c a u se m a n y i c o n s c a n h a v e c o m m o na t t r i b u t es . I c o n s a r e a ls o s m a l l a n dthere fo re use l e s s space (Sears 1993) ,l es s t h a n 5 d e g r e e s o f ar c . A n o t h e ra d v a n t a g e o f i c o n s is t h a t r e c o g n i t i o ni s f a s te r fo r p ic tu res than fo r t ex t (Ben-b a s a t a n d T o d d 1 9 9 3 ). T h i s m a k e s i teas ie r fo r the nov ice to l ea rn a sys tem.S t u d i e s a l s o s h o w t h a t i c o n s h a v es m a l l e r e r r o r r a te s t h a n t e x t u a l i n t e r -f a c es a n d t h e s a m e a s fo r m e n u i n t e r -

f a c es (S e a rs 1 9 9 3 ) . C o n v e r s e l y t h o u g h ,e m p i r i c a l s t u d i e s h a v e s h o w n t h a t ,c o u n t e r i n t u i t i v e l y , i c o n s d o n o t l e a dt o g r e a t e r i n c r e a s e s i n p e r f o r m a n c e .

3 . H i g h l i g h t i n g : B e s i d e s co l o r, t h e r e a r es e v e ra l o t h e r m e t h o d s o f h i g h l i g h t i n gi n c l u d i n g r e v e rs e v i d eo , b r i g h t n e s s ,u n d e r l in i n g , a n d f l a sh i ng . T h e m o s tc o m m o n u s e o f h i g h l i g h ti n g i s r e ve r sev i d e o t o i n d i c a t e a n i t e m t h a t i s c u r -r e n t l y s e l e c t e d . G U I s u s u a l l y u s eb r i g h t n e s s t o s h o w w h i c h i t e m s a r e n o ta c t i ve a t a g i v e n t i m e . U n d e r l i n i n g i se f f ec t i v e i f i t d o e s n o t i n t e r f e r e w i t h t h eleg ib i l i ty o f charac te r s . F lash ing wi l lb o t h g e t a t t e n t i o n a n d a n n o y i f t h eu s e r c a n n o t t u r n o f f t h e f l a s h i n g .T h e r e f o r e , o n e s h o u l d u s e f l a s h i n go n l y t o c o n v e y a n u r g e n t n e e d . T h eA p p l e M a c i n t o s h u s e s f l a s h i n g t o s i g -n a l o n l y p r o g r a m o r d a t a d e s t r u c ti o n .R e g a r d l e ss o f w h i c h t y p e o f h i g h l i g h t -i n g , o n e n e e d s t o a p p l y i t c o n s e r v a -t iv e ly . O v e r u s e o f h i g h l i g h t i n g c a u s e sc o n f u s i o n a m o n g u s e r s a n d d e f e a t s i t sp u r p o s e . A d d i t i o n a l ly , i f o n e h i g h -l i g h t s t h e w r o n g i n f o r m a t i o n , t h e u s e rh a s m o r e d i f f i c u l t y d e t e c t i n g t h ei m p o r t a n t i n f o r m a t i o n ( H e l a n d e r1 9 8 8 ) .

I n f o r m a t i o n S e q u e n c i n gO n e n e e d s t o l a y o u t a s cr e e n i n a m a n n e rtha t a l lows the use r to eas i ly f ind a nyi n f o r m a t i o n o n i t . M o s t d e s i g n e r s a d v o -c a t e t h e u s e o f o n e t h e d e f a c t o G U Is c r e e n s ta n d a r d s . T h i s i s b e c a u s e m a n yu s e r s n o w e x p e c t c e r t a i n m o d e s o f o p e r a -t i o n i n a l l G U I s . F o r e x a m p l e , m o s t u s e r se x p e c t t h e t o p o f s cr e e n t o c o n t a i n t h eh e a d i n g s f o r t h e p u l l - d o w n m e n u s . T h et o p r i g h t i s t h e d e f a u l t l o c a t i o n f o r i c o n srepresen t ing the d i sk ava i lab i l i ty . In theM a c i n t o s h G U I , t h e b o t t o m r ig h t c o n -t a i n s t h e t r a s h i c o n s u s e d f o r d e l e t i n gf il es . W i t h i n a w i n d o w , t h e r e a r e a ls om a n y s t a n d a r d m o d e s . A w i n d o w t it le isusua l ly a t the top . Sc ro l l ba r s a re on ther i g h t a n d b o t t o m f o r v e r t ic a l a n d h o r i -z o n t a l w i n d o w m o v e m e n t . A b o x f o rc l o s i n g t h e w i n d o w i s a t t h e t o p l e f t .I c o n s f o r r e s i z i n g t h e w i n d o w a r e a t t h ef o u r c o r n e r s ( H e l a n d e r 1 9 8 8 ) . S t u d i e ss h o w t h a t m o s t u s e r s i n i t i a l l y s c a n t h es c r e e n s t a r t i n g a t t h e u p p e r - l e f t c o r n e r .T h i s c o r n e r s h o u l d b e t h e o b v i o u s s t a r t -i n g p o i n t f o r ap p l i c at i o n s i n v o k e d f r o mw i t h i n t h e w i n d o w . T h i s p e r m i t s a l e f t-t o - r i g h t a n d t o p - t o - b o t t o m r e a d i n g ,w h i c h i s s t a n d a r d f o r W e s t e r n c u l t u r es .

T h e o p t i m u m s e q u e n c e f or s c r ee n p r e-s e n t a t i o n s i s a c o l l e c t i o n o f v a ri o u s f a c -to r s , inc lud ing :1 . S e q u e n c e o f u se : O n e n e e d s t o p r e s e n t

t h e u s e r t h e i n f o r m a t i o n i n t h e o r d e rt h a t t h e u s e r w i l l p r o b a b l y u t i l i z e it .

2 . C o n v e n t i o n a l U s a ge : I f a c o m m o nc o n v e n t i o n i s i n g e n e r a l u s a g e , t h eG U I d e s i g n s h o u l d c o n t i n u e u s i n g i t .F o r e x am p l e , i n t h e s t a n d ar d w i n d o wl a y o u t , t h e f i le o p t i o n i s u s u a l l y t o t h ef a r le f t o f t h e m e n u b a r .

3 . I m p o r t a n c e : T h e d e s ig n e r n e e d s t op l a c e t h e m o r e i m p o r t a n t i n f o r m a t i o ni n a p r o m i n e n t l o c a t i o n . F o r e x a m p l e ,i f s e v e ra l e n t r ie s a r e p o s s i b le , t h e G U Is h o u l d l e a d o f f w i t h t h e r e q u ir e d o n e sa n d e n d w i t h t h e o p t i o n a l o n e s .

4 . F r e q u e n c y o f us e : O n e s h o u l d p l a c et h e m o s t f r e q u e n t ly u t i li z e d c o m -m a n d s a t t h e b e g in n i n g . F o r e x a m p le ,i n a m e n u l i s t , t h e m o s t f r e q u e n t l y u t i -l iz e d c o m m a n d s s h o u l d b e a t t h e t o pof the l i st .

5 . G e n e r a l i t y v e r s u s S p e c i fi c i ty : T h em o r e g e n e r a l i t e m s s h o u l d p r e c e d e t h em o r e s p e c i f i c i te m s , e s p e c i al l y w h e nthere i s a h ie ra rch ica l r e la t io nsh ipa m o n g t h e d a t a .

6 . A l p h a b e t i c a l o r C h r o n o l o g i c a l : I f t h e r ei s n o o t h e r r u l e s f o r o r d e r i n g d a t a e l e -m e n t , t h e n o n e s h o u l d a d o p t s o m eo t h e r t e c h n i q u e s u c h a s a n a l p h a b e t i c a lo r a t e m p o r a l l i s t in g . C a r d ( H e l a n d e r1 9 8 8 ) s h o w e d t h a t s e l ec t i on t i m e w a sf a s t er f o r a l p h a b e t ic a l t h a n f o r a n yo t h e r f u n c t i o n a l g r o u p i n g . T h e g o a l o fa n y G U I i s t o a l l ow t h e u s e r t o w o r kt h r o u g h t h e c o m p u t e r a n d a p p l i c a t i o nt o c o n c e n t ra t e o n t h e p r i m a r y c o g n i -t i v e t a s k. T h e u s e r s h o u l d n o t b e c o n -c e r n e d w i t h t h e u s e r i n t e r f a c e . A n ya t t e n t i o n d e v o t e d t o t h e i n t e r f a c ei n t e rf e r e s w i t h t h e m a i n t a s k ( B e n b a s a ta n d T o d d 1 9 9 3; N o r m a n 1 9 8 8) .

R a m i f i c a t i o n sW h a t a r e t h e r a m i f i ca t i o n s o f G U Id e s i g n ? O n e c o n s i s t e n t r e s u l t i s t h a t a ni n c r e a s e d o p e r a t i o n a l k n o w l e d g e t r a n s f e rb e t w e e n a p p l i c a t i o n s r e d u c e s t r a i n i n gc o s t s ( H a r d i n g 1 9 8 9 ) . T r a i n i n g c o s t s a r eu s u a l l y o n e t o t h r e e t i m e s t h e c o s t o f t h ea c t u a l s o f t w a r e a n d h a r d w a r e ( B o e r i a n dM a r t i n 1 9 9 4) . A g o o d G U I d e s i gnr e d u c e s r e q u i r e d t r a i n i n g t i m e t o 2 0 - 3 0h o u r s f o r a u s e r t o l e a r n a n a p p l i c a t i o n( C o m a f o r d 1 9 9 3 ) . F o r b u s i n e ss e s , th i sm e a n s t h a t a g o od G U I s av es m o n e y a n d

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time. Additionally, a goo d GUI improvesthe user's percept ion o f the application.Th e user's first 15 minute s of usage for-mulates the lasting impression of anapplication.C o n c l u s i o nThe p rimar ygoal of a GU I is to allow theuser to concentrate on the task at hand.To do this, the GUI must make the inter-face between the human and the com -puter seamless. Mod ern GUI s adhere toone o f three de facto standards, which arethe Apple Macintosh, the IB M SAA, andthe MI T X-Windowing System. Thesestandards are not perfect, but they aregood enough to preclude major devia-tion. Future GUIs will probably utilizeone or more of these standards unlessmajor perfor mance enhancements result.Utilizing key psychological factors, GU Idesigners can achieve a seamless com-puter hu man interface. The three pri-mary h uma n factors that directly affectGU I design are visual acuity, the limits ofabsolute memory, and the grouping ofinformation. At about 19 inches from anobject, a person's visual acuity is about 5degrees of arc. Th ere appears to be a limitto absolute memo ry of about 7 items.Grouping of information based on theGestalt principle appears to aid in infor-mation processing. Use of these factorsresult in GUI design principles that gov-ern the amoun t o f information topresent, the proper way to group thisinformation, and the proper placementand sequencing of this infor mation onthe screen. A good G UI should presentinformation that is contextual and con-sistent. It should av oid unnecessary detailand use concise wording to conservescreen space. I f familiar data for matsexist, the GUt should utilize them. AGUI needs to group information usingcolor to associate like items. Graphica lboundar ies are a very effective means togrou p like items, especially icons. Ot herhighlighting techniques include reversevideo, brightness, underlining, and flash-ing. One needs to sequence informationon the screen to facilitate the user. T hepresentation of information shou ld fol-low the sequence that the user needs it.Co mm on information needs to be inco mm on locations across windows andGUIs. The most important informationneeds to precede the lesser importantinformation. Frequently utilized infor-mation or commands need to be in the

most prom inent location. The mor e gen-eral items should precede the more spe-cific items. I f no othe r or dering exists,one should alphabetize. The ramificationof good GUI design results in reducedtraining time and im proved perfor-mance. Reduced training time meanslower costs and improved user percep-tions. Bad GUI design prevents the userfrom concentrating on the primary cog-nitive task. This results in user frustra-tions, decreased performance, highercosts, and possibly produ ct an d market-place failure. When designing GUIs, oneneed to keep the objectives of the GU I inmind and to generally avoid needlesscomplexity (Marcus 1992). One mustavoid useless innov ation an d concen trateon improvements that enhance perfor-mance. Future trends in GUIs are towardvoice recognition and hypertext format-ting language (Hayes and Barab 1989;Horton 1990). The hypertext trendallows the user to move directly fromdata and concepts in one application tosimilar data and concepts in other appli-cation. These trends will further removethe GUI as an obstacle between the userand the task.R e f e r e n c e sBaddeley, Alan. 1994. The Magical NumberSeven: Still Magic After All These Years?Psychological Review. Vol. 101. No. 2:353-356.Benbasat, Izak and Peter Todd. 1993. An

Experimental Investigation of InterfaceDesign Alternatives: Icon vs. Text andDirect Manipulation vs. Menus. I n te rna -t i o n a l J o u r n a l o f M a n - M a c h i n e S t ud ie s . Vol.38:369-402.Betts, Mitch. Standard GUIs Make Sense.C o m p u t e r w o r l d . Vol. 28. No. 11:75-76.Bonsiepe, Gui. 1993. Interpretations ofH um an User InteoGce. Visible Language.Vol. 24. No. 3:262-285.Boeri, Roberts J. and Martin Hensel. 1994.Mar Hum an Factors in Business CD -ROMTitles. C D - R O M P r o )~ s si on a l. Vol. 8. No.2:107-108.Comaford , Christine. Graphical User Inter-faces: Keep Them Sleek and Simple. C o m -p u t e r w o r M . Vol. 25. No. 16:37-40.Harding, Bruce A. Windows & Icons &Mice, Oh My! T h e C h a n g i n g F a c e o f C o m -pu t ing . Fron t ie rs i n Educa t ion Con fbrence1989:19 h Annual: 337-342.Hayes, Frank and Nick Baran. A Guide toGUIs. B y t e V o l . 4. (July 89):250-257.Helander, Martin ed. H a n d b o o k o f H u m a n -Com pute r I n te ract ion . New York: 1988.

Hopkins, Don. Paper from The X-WindowsDisaster. Undated from t he U N I X H a t e r sPSbb-Site. Accessed May 1996.Horton, William. 1990. Visual Rhetoric forOn-line Documents. IEE E 7~ansac t ions onPro fkss iona l Comm unica t ion . Vol. 33. No.3:108-114.Hubona, Geoffrey S. Evaluating. 1995. UseInterface Design with Belief Constructs.

S y st em s S c ie n ce s , 1 9 9 5 A n n u a l H a w a i i l n t enational Conference. Vol. 4:700-709.Lin, Yi Bing and Dan Daly. 1994. A FlexiblGraphical User Interface for PerformanceModeling. M A S C O T S 1 9 9 4: M o d el in g ,Ana lys i s, an d S imu la t ion I n te rna t iona l

I /brkshop: 193-199.Marcus, Aaron. The Future ofAdvanced UseInterfaces in Product Design. T R O NProject, 1992 Symposium: 14-20.Miller, George A. 1956. The Magical Num-ber Seven, Plus or Minus Two: Some Limiton Our Capacity for Processing Informa-

tion. Psychological Review. Vol. 101. No.2:343- 352.Norman, Donald. The Psycho logy o f EverydaThings. New York: Basic Books: 1988.Reiterer, Harold. The Development ofDesign Aid Tools for a Human FactorBased User Interface Design. Sys tems , Manand Cyberne t i c s , 1993 In te rna t iona l Cona~ence~ 361-366.Sarna, David E. and George J. Febish. WhaMakes a GUI Work? D a t a m a t i o n Vol. 4.(July 15 1994):29f.Sears, Andrew. 1993. Layout Appropriate-

ness: A Metric for Evaluating User InterfacWidget Layout. IE EE 7~ansac t ions on So f tware Engineering. Vol. 19. No. 7:707-720Shiffrin, Richard M. and Robert M. Nosof-sky. 1994. Seven Plus or Minus Two: ACommentary On Capacity Limitations.Psychological Review. Vol. 101. No. 2: 357361.Wickens, Chris topher D. EngineeringPsycholo g y a n d H u m a n P e ~ b rm a n c e. 2d ed. Harpers: New York: 1992. p. 24-109, and 116160.Anonymous. 1995. I gHndows 95 Annoyanceshttp://www.creativelement.com/win95ann. Dated 15 November 1995.A u t h o r ' s A d d r e s sDepa rtm ent of Electrical Engineeringand Com puter ScienceUnited States Military Acade myWest Point, New York, 10997, USAjansen@exmail.usma.edu

2 6 A p r i l 1 9 9 8 V o lu m e 3 0 , N u m b e r 2 S I G C H I B u lle tin