ML17321A661

Rev 0 to Man-Machine Interface Design Basis Document:Info Coding for Computer Display Sys.

ML17321A661
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Issue date:	10/31/1980
From:	ECKERT S, WOODS D D WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
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HAN-HACHINE INTERFACE DESIGNBASISDOCUHENT:

INFORHATION CODINGFORCOHPUTERDISPLAYSYSTEMSREV.0P.D.MoodsSS.EckertOctober,1980g506i004io 850581PDRADOCH05000Si 0ltl SummaryIntroduction Characteristics ofaGoodCodeCodingFunctions CodescanaidsearchprocessCodescanamplifyinformation Codescanorganizedispersed, information Codescanaidinformation reduction CodingDimensions Symbology Alphanumeric SizeLineStructure Brightness Highlighting Orientation BlinkTime-varyingcodesAuditoryCodesColorColorCodingStrengths CautionsAssociated withColorCodingColorCodeAl,phabet SizeRecommended ApproachtoColorCodingInteractive Techniques Candidates forCodinginProcessControlReferences

2.0 Introduction

Thisdocument, sponsored bytheControlRoomandComputerDevelopment groupoftheStrategic Operations

Division, presentsHumanFactorscriteriaforthedevelopment ofinformation codingschemesincomputerdisplaysystems.

0 Information displaysystemsshouldsupportaquickandaccuratetransferofinformation totheuser.Codinginformation isonetechnique available tothedesignertomeetthisgoal.Codingmethodsshouldbeincorporated whenanyofthefollowing threeconditions areapplicable:

~whenadensepresentation ofinformation isrequired~whenthetaskrequirements aredifficult orprecisewhenaquickresponsetimeisessential Codingtechniques shouldbeviewedasoneoptionamongmanytofacilitate information processing andinterpretation.

Thearrangement of"theinformation andthemodeofpresentation willhavedramaticimpactsoninformation transfer.

Onecannotincorporate codingintobadlyformatted displaysandexpectdramaticoperational improvements.

Therefore.

codingshouldbeoneofthelastelementsdisplaydesign-thebestformatshouldbedeveloped forpresenting theinformation totheoperatorpriortoincluding thecodingfeatures.

Characte'ristics ofaGoodCodeDetectability

-Anystimulususedinthecodingofinformation mustbedetectable orperceivable bytheuser.Discriminability (1)Theusermustbeabletodiscriminate betweendifferent codingtechniques; (2)withinagivencodingmodality, theusermustbeabletodiscriminate different valuesorstates.Thenumberofdiscriminable stimuliwithinacodingdimension changesacrossdimensions andofthetypeoftask-eitherare]ativeoranabsolutediscrimination.

Aperson'sabilitytodetectdifferences betweenstimuli(tomakearelativejudgement) ismuchkeenerthanone'sabilitytodetectadifference witharemembered comparison.

Introducing reference pointssuchasperceptual anchorscanincreasetheeffective resolution withinacodingclassbyallowingrelativejudgements.

~Compatibility

-Thecodechosenshouldbecompatible withthetypeofdataorinformation beingcoded.Thusaqualitive code(symbols, color)shouldbeusedforqualitive data;aquantitative codinotechnique (length,intensity, size)isbetterforpresenting quantitativeinformation.'Forexample,colorcouldbeusedtocodeaquantitative dimension suchastemperature asinaninfraredphotograph.

Thisisagoodwaytorepresent differences intemperature.

However,'his isapoorwaytoindicatetemperature valuessincethereisnoobviousrelationship betweencolorandquantity.

Mhenthevalueofadatapointrepresented bygreendoubles,whatcolorshouldresult?oAssociation

-Symbolcodesshouldphysically represent theactualobjectbeingportrayed.

~Standardization

-Theuseofcodesshouldbestandardized throuahout thedisplaysystemandthesurrounding userworkstation.Ifredisusedasanalarmcolorintheindicator lightsaboutthecontrolstation,redshould.alsobereservedasanalarmcolorontheCRTdisplaysifatallpossible.

~Redundancy

-Itisadvantageous touseredundant coding:twoormorecodingdimensions areusedincombination todesignate aparticular condition.

~Inaddition, acodeshouldnotintroduce fatiguing ordistracting effects',

anditshouldberelatively easytoincorporate intothemachinesystem.Iftheseguidelines aremet,thecodingschemeadoptedshouldbeeasytointerpret withlittleintercode confusion.

CodingFunctions 1.CodescanaidsearchrocessThetimetosearchasetofcandidates foraparticular targetincreases assetsizeincreases.

(Steinberg

).Therefore searchtasksbecomemoredifficult (takelongerandaremoreerrororone)astheinformation densityofadisplayincreases.

Codescanincreasesearchspeedandaccuracythroughacategoryeffect.Mhenthetargetisamemberofclearlydefinedsubsetofthetotaldisplay,searchspeedahdaccuracvisafunctiononlyofsubset"sizenotofthetotalnumberofdisplayelements(Egeth,Jonides,and6NMall,1872).Thisistrueaslongasthenumberofdifferent subsetsorcategories issmall(lessthan4).Forexample,searching foraredtargetamonga'fewredandmanywhitedisplayelementsisfasterandmoreaccuratethansearching forthesametargetwhenalldisplayelementsaremonochromatic.

In.general,itemsofagivencategoryaredetectedfasterandmoreaccurately againstabackground consisting ofitemsfromadifferent

categoryascomparedtoabackground ofitemsfromthesamecateaory(Oeutsch, 1977).2.Codescanamlifinformation.

Codesfulfillahighlighting functionbyattracting theuser'sattention toimportant information.

Forexample,codes,canbeusedtoemphasize anomalies.

andabnormalstates.3.Codescanoranizedisersedinformation.

Codingtechniques areparticularly valuabletointegrate information thatisspreadacrossthedisplaypageasopposedtoinformation thatisalreadyorganized by'rows,columns,orquadrants.

4.Codescanaidinformation reducti'on Aflexible.

displayshouldfacilitate severaltypesofviewingtasks;whatisrelevanttoonetaskmaynotberelevanttoanother.Theusermayberequiredtoblockoutinformation thatisnotper-tinanttothetaskathand.Displaysshouldbestructured sothatinformation reduction isagatingtaskratherthanacondensation task.Gatingrequiresonlythattheuserignoreirrelevant stimulusdimensions.

Thisactivityispartofnormalandoftenautomatic perceptual mechanisms thatthebrainroutinely usestopreventinformation overload.

Condensation tasksplaceaburdenontheuser'scognitive capacitysincetheinformation mustbecombinedincomplicated ways{Norse,1979;Posner,1964).

Forexample,redtriangles andbluesquaresmayhavetobementallygroupedtogetherandtreateddifferently fromagroupofredsquaresandbluetriangles.

Anotherwaytoaidinformation reduction istostructure displaysintoforeground andbackground.

Thisapproachtakesadvantage ofautomatic perceptual processes whichdifferentiate figurefromground.Whenimportant andunimportant orreference information (forexamole,scalesorgridpatterns) isundistingushed, theusermaysufferfrominformation overloadorhemayberequiredtouseupmentalcapacityinordertodistinguish theprioritylevel.Justasaninformation hierarchy supplieslayersofinformation fromthegeneraltothdetailed, individual displaysshouldprovidelayersofinformation goingfromreference orbackground toimportant tocriticalinform-ation.Notethatinformation reduction techniques areonemeansforkeepingdisplaydensitywithintheoptimumrange.Inorderforthedisplaydesignertomatchhiscodeselection andanoverallcodingschemetotheuser'stasks,hemustdetermine what1information theuserneedstoextractfromeachdisplay.'his canbeaccomplished throughataskanalysiswhichdetermines theuseractivities eachdisplaymustsupport.CodingDimensions Symbology (Shape).Graphicorpictorial symbolsandshapesasdataidentifiers.

Symbolsshouldrepresent theobjectbeingportrayed.

Thisiscallediconiccodinganditreducestrainingtimeascomparedtoarbitrary symbolcodes.,Iconiccodingalsoheightens symbolrecoqnition andstrenqthens theassociation betweenthesymbolandtheactualobject.

Thiseffectincreases thetransparency oftheinterface.

Symbolsshouldbesimplebutdetailedenoughtobediscriminable andtopromptassociations andaccurateidentification.

Thenumberofshapesthatcanbecorrectly identified isquitelarge,limitedprimarily bytheabilityofanobservertoassociate thesymbolswiththecorresponding objects.Thisabilityisdependent uoonthefidelityofthesymbolshape,usertraining, andstress(Oda,1977).Generally amaximumof10to15different symbolsarerecommended formostapplications.

2.Alphanumeric Alphanumeric codingisfrequently usedtopresentquantitative information, tagnumbersorsimilaridentifiers.

Anyabbreviations oracronymns shouldbereadilyassociated withthetotalword,andtheyshouldbestandardized throughout thesystem(bothonthecontrolpanelandonallCRTdisplaypages).Alphanumerics shouldideallybethreecharacters orlessbecauseofthepropensity ofoperators.

Tominimizetransoosition errorsinidentifiers suchasiagnumbers,alphabetic characters orotherseperators shouldbeinterspersed amonglongrunsofdigits.3.SizeTheactualsizeofacharacter orsymbolcanbevariedtoconveyinformation totheuser.Anoperatorcandifferentiate betweenapproximately fourorfivedifferent sizevariations onanabsolutebasis.However,formostapplications, twosizeoptionsarere-comnended, enablingausertoreadilydiscriminate andidentifythesizebeingpresented.

Logarith<<c

.(constant ratio)sizevariations aremoreaccurately differentiated thanlinear.

Sizecodingisbestusedtodifferentiate betweeninformation ofdiffering importance orsymbols/components indiffering states(i.e.,onoroff).Onedrawbackofsizecodingisthelargerspacerequirements topresenttheinformation.

4.LineStructure.

Varyinglinestructures canbeusedtoconveydifferent messagestotheuser.guantitative information canbecoamunicated bvvaryingthelengthorthewidthoftheline.gualitative information canbeconveyedbychangingthetextureoftheline(solidvsdashedvsdotted).Linestructure codingcanbeeffectively usedongraphicdisplaypresentations suchasmimicdisplaystodifferentiate betweenflowandnoflowstatesforthefluidorelectrical currentlinesofthediagram.Alinestructure codecanbeexpandedintoatexturecode.Textureworkswellasacodeforlargefieldssuchasareasonagraphortoindicatestatesonlargesymb'ols.

5.Brightness/Itensity ManyCRTsystemshavemultiplelevelsofintensity whichcanbeusedindisplaycoding.Ingeneraltwolevelsofintensity arerecomnended fordisplaycoding.Theeffectiveness ofbrightness asacodingmethodisdependent uponthecontrastofthedimmerlevel.Ifthiscontrastispoor,fatiguemayresultandinformation maybeoverlooked.

Ifthecontrastofthelow-intensity optionisadequate, brightness codingcanbeprofitably usedtosuppressback-groundorlessimportant information, likegridlinesandlabels, whichareonlyinfrequently requiredbytheexperienced user.6.Highlighting Monochromatic displaysprovidesomestandardhighliqhting techniques whichcanbeusedtodesignate important information onadisplayorattractausertoachangeofstaterequiring hisattention.

Underlininq orunderscoring arecommonlyavailable forhighlighting information.

Videoreverseisaneffective tooltoattractanoperator's attention toanimportant pieceofinformation.

Specialsymbolscanbeusedtodesignate important information (i.e.arrowsorbullets);

Criticaldata.valuescanhaveboxesorcirclescircumscribed aroundthemtohighlight themtotheuser.Allofthesemethodsofhighlighting andattention-gettinq facilitate userinterpretation ofhighdensity,complexdisplaypresentations.

7.Orientation Theangularorientation ofasymbolorlinecanbevariedto.conveyinformation totheuser,forexampleclocksanddials.Orientation isasuitablecodingtechnique aslongasonlyrelativediscriminations arerequired.

Errorratesforabsoluteidentification ofanglearehighformorethanafewcategories.

8.FlashRateorBlinkCodingBlinkcodingisaneffective attention gettingtool.Howeverblinkingamessagereducesitsreadability (flashing anadjacentsymbolcansolvethisproblem).

Blinkingalsotendstobeveryfatiguing andannoyingtousers.Therefore blinkcodingshould/onlybeusedtocalltheuser'sattention tocriticalevents.Flashratesshouldbebetween1and5Hz(3Hzisatypicalrecommendation) andonlyonerateshouldbeused.Becauseofthedrawbacks toblink'I coding,eventacknowledge orblinksuppression shouldbequicklyavailable totheuser.9.Time-varying codesAnimation isapowerfulwaytodisplaytime-varying data.Insteadofrepresenting timewithaspatialdimension onagraph,simulation timecanbeusedtoencoderealtime.Fasttime,slowmotionandfreezeframetechniques canhighlight information thatwouldotherwise be'difficult fortheusertoprocess.Howeverthedesignermustbecarefulherebecausechangesintimeframecanalsodistorttherealtimeinformation.

Anotherexampleoftimecodesis'displayaidingwhichshowsatrailofdisplacements thatfadeovertime,sothatamovingobjectorachangingdatapointleavesatrailoffadingfootprints whichindicates itspositionorvalueintherecentpast.Notethatthisexamplecombinesbrightness codingwithatimecodeto'communicate trendinformation totheuser.Thecriticalvariablefortime-varying displaysisthedurationoftheblankintervalbetweenframes.Notimegapisbestandifthegapexceeds1second,memoryaidingmaybenecessary toprovidecontinuity.

10.AuditorycodesTheauditorymodalityisusuallyunderestimated asacodingmedium.However,severaldimensions ofsoundsareavailable toconveyinformation totheuserinaneffective way(frequency,

itensity, quality,pattern,rhythm).Theearpossesses tremendous powersoftemperalresolution (Green,1978).Auditorycodesshouldtakead-vantageoftheseabilities.

Becauseauditorycodesareusuallyusedaswarningsignals,amoredetaileddiscussion ofauditorycodingtechniques willbereservedforaseparatereportonHumanEngineering criteriaforalarmandannuciation systems.11.ColorColorisnottheultimateanswertoallcodingproblems.

Colorshouldnotbeusedtotheexclusion ofachromatic codingmethods,rathertheyshould.beusedtosupplement andcomplement oneanother.ColorCodingStrengths

~Colorcanincreasedetection accuracyandsneedbyreducingthesizeofthesettobesearched.

Thisistrueonlywhenlessthan4colorsoccuronanygivendisplay.-

Forlargeralphabetsizes,colorcodingcanactuallyincreasesearchtimes(Christ,1975).Colorisagoodattention focuserwhenusedjudiciously.

Theutilityofcolorcodingforhigliohting information isenhancedwhenthereareonlyafewcolorspresented onthedisplaysothatachangeincolorfromanormalcondition toahighlighted condition willbereadilydetectable.

Colorisaneffective toolforintegrating physically separatepieces,ofdata.Colorcodeddispersed datacaneasilybyorganized intoasingleperceptual unitforfurtheranalysisasagroup.~Colorcanbeusedtoseparatedisplaysintofigureandgoundareas.

oColorisaneffective meansofinformation reduction byseoarating foreground andreference information.

Sidorsky(1979)foundthatcolorwasofvalueprimarily forgroupingdataatafirstlevelofanalysis, i.e.theinitialgroupingofwhichdatapiecesarerelatedtowhich.HoweverSidorskyfoundcolorwasnobetterandperhapsworsethanshapeoralnhnumericcodingforsubsequent levelsofanalysis.

Therefore, colorcodingcanbeeffectively usedtostructure displayed information forsubsequent analysisandinterpretation.

Colorcodingcanbeusedtoenhancenaturalrepresentations.

Insomeapplications coloristhemostdesirable codingmodalitybecauseitmostnaturally represents thephysicalrealitybein@encoded.Forexample,thered/yellow/green colorassignment" aremostnaturally associated withdanger/caution/normal designations thanother,achromatic codingdimensions.

Colordisplaysareoftensubjectivelv oreferred overcorn"letel:

achromatic displays(Grist,1975;Chase,1970;Schutz,1961).Colorbackgrounds aswellascolorsy..bnlscanLeusedtoco"einformation.

Forexample,changingthebackground from.blacktodarkbluecouldbeusedtoindicatechangesinplantorsystemmode.However,displaysshouldbeevaluated withthecolor,background becauseofpossibleflickereffectswhichincreaseasfieldsizeincreases andbecauseofpossiblecontrasteffectsonlegibility.

~~CautionsAssociated withColorCodinq~AbnormalColorVision?tisestimated that8Xofthemalesand0.4".ofthefemalepopulation posssssomeformofabnormalcolorvision.Themostcommonformofcolordeficiency i'saromalous trichromat',sm whe~eapersonissensitive tothreechromatic stimulibutthei.matchesdonotfallwithin'he normalrangeofvar',ation.

Themo.tcordondeficiency entails.aweakgreenresponse(deuterar o"..aly)whichaccountsfor4.9Xofthemalesand0.38Kofthefemales.Aweakredresponse(protaronaly) accountsforanother1,;ofthe~alepopulation.

potential solutiors includescreening

'usersbycolordeficiencies andchoosin".

choosingcolorswhicharenotaffectedbvthemorecomonformsofabnormalcolorvision.~HardCoInapplications wherehardcopiesofdisplaysarerequired, allcolorcodingmustbusedredundantly withmonochromatic technioues.

DeceasedRsolutionDisplayresolution canbereducedoncolorCRTsbecauseoftherequirement toplacethreephosphordotsofdifferent colorsonthedisplayface.Tocompensate forthis,character andsrm'-olsizesmustbeincreased toaccurately conveycolorinformation totheuser.Misreistration Theneedtoalign-3beamscancausemisregistration problems.

Periodicadjustments willberequired.

~~No<seCode.Theveryfactorswhichcontribute tocolor'seffectiveness asacodemakeitarealnuisanceandhinderance totheuserifnotaporop-riatelyused.Whennotusedjudiciously, colorcodingcan,infact,degradeperformance.

SoectialSensitivit!

Functio.".s.

Theey~isnotequallysensitive toal';w<svelengt"s (s";e."i"ure1).Thismar<sthatdiff::r=-nt colorso<idnticalpiyicalirt.=nsii."swillnotappearequallybright.Whenavarietyofcoloursareus.dinthesampictur,therelativeintensity lev.lofthv.riouscoloursshouldbeinaccordance withthespectralsensitivitv o.theeyeinordrtoavoidunintendddominance ofonekindofinformation overanothr.

.However,notethatthesebrightne'ss cuesasafunctionofwavelength canbeusedbycolor-d~ficient individuals todistinguish different colors.Colorhotoicvision)encetionhasahiherthreshold thanachromatic (scotoicvision)ercetion.Perceived colorswillchangeandmaybecomeachromatic ifthedisplayintensity istoolow.Thismeansthathighersymbolandcharacter luminance isrequiredforcolordisplaysthanachromatic ones.Ambient?11umination Reuirements.

ColorCRTsaregenerally moresensitive toambientillumination.

Contrastorluminance areusuallylessforcolorversusmonochromatic CRTsandcorresponding decreases intheintensity ofambientillumination mayberequired.

Thecoloroftheambientillumination canalsodramatically effecttheperceived colorofaCRT.Theselection ofcolorsforinformation codingshouldbemadeinasituation whichstimulates boththecolora'ndintensity oftheanticipated ambient'illumination intheoperational setting.ColorContrast.

Whencolordisplaysareviewedforlongtimeperiodsapparenthueandsaturation canchangeduetocontrasteffects.Thevisualsystemprocesses colorinformation inopponentpairs:red-green, blue-yellow andblack-white.

Prolonged viewingofonecolorreducestheeye'ssensitivity tothatcolorandincreases theeye'ssensitivity tothecomplementary color.Simultaneous contrasteffectscanalsoproducechangesinperceived colorsduetotheinfluence ofthecolorofsurrounding areas.Contrasteffectswillbemostpronounced when h

~~therearelarge,coloredfieldsonthedisplays.

~Chromatic Aberration.

Thelensoftheeyefocuseslightordifferent wavelengths atjdifferent depths.Thisiscalledchromatic aberration.

Iftherearemanydifferent wavelength colorsonagivendisplay,theeyecannotfocusallofthecolorsatthesametime.Theaccomodation (focusinq) mechanisms willcontinually adjustinordertoattempttomaintainproperfocus.Thiseffectisonemajorsourceofeyefatigue.Totheextentpossible, colorsofverydifferent wavelengths shouldbeavoidedindisplaysthatwillbeviewedforlongperiodsoftime.ThisproblemisthereasonHumanFactorsguidelines oftenrecommend miniraluseofbluecolors.ContrastRatioContrastratioisnotindependent offoreground andbackground colors.Figure/ground colorrelationships canincreasetheeffective contrastratioandtherebyincreaselegibility.

Howeverapoorchoiceofcolorscandestroyvisibility; forexample,darkblueonablackgroundisvirtually invisible.

Theremaybetimeswhenlessvisiblesymbolscanbeuseful.Forexample,softwareconsiderations mayrequirethatacertainsymbolmarkeachtabpointonadisplay.Choosingapoorlyvisiblesymbolcolorcaneffectively gateoutthisirrelevent information.

s~~~Tes~troons.

d~~i;alas.BecauseofillcAnation, luminance, contrasteffectsandchromatic aberration itisessential thatproposeddisplaysbetestedontheactualdisplaymedium,i.e.ontheCRTchosenfortheaoplication, intheappropriate environment.

Thereisnoreasonthatacoloreddrawinqofproooseddisolayswillcorresoond atalltotheactualCRTdis-lay:.

AC~Tdisplayisalihte~i'.terandadrawn,"i"sa4"hrf!e=t'r.t:letWOCaSs'SdOnOtnrOduCeperC=ptiOnS t;:ataieautOnatiCasl" equ-'.al~-t.

0herComments.

Ifsinglefailurecriteriaareimnortant, cZeosingcolorsbasedonibea;.scani~creaserdurdancy.

Howev=-rcult-;p'e

'"earncolo:s,p=rticusarl" w'.".ite, increasecon:erqencs p.o~le~s"-hichdecreaseI."-effective contrastofthdisplay."olorC".d=Ap,a.e-.Siz:-.h"r"i.-ata~d".ncy fordis"l~y".e"i-ners t~u"-e"o"ero'.orsthorn'soprationally w:rrant;".d.

D:s'ig.".ers;.hcu:d:o-.

f::e:cm-elledtutilizedallofthecolorsthatagivenCRTprovides.

Thenumberofcolorsthatcanbediscriminat daccurately dependson'avelen~t.".,

saturation, bri~htness, illumination, symbolsizeandcontrasteffects.Whilehundredsofcolorscanbediscriminated onarelativebasis,Haeusin."

(1976)foundthatonly4colorsworereliablydiscr'.min-t:d onanabsolutebasisusingtestdisplaysthataretypicalofcurrentCRTdisplays.

Becauseofthisresultandbecauseofthecautionnotedintheprevioussection,thecolorcodealphabetshouldnotexceed3or4hues(Myszecki andStiles,1967;Burdicketal,1965).Recomnended ApproachtoColorCodingTherearemanycodingschemeswhichcanmeetHumanFactorscriteria.

Thefollowing isonegeneralapproachthatfulfillsthesecriteria.Colorshouldbeusedtoorganizedisplaysandfocustheuser'sattention onimportant information.

Ananalogycanbemadebetweenlevelsofaninformation hierarchy andlevelsofacolorcode.Aninformation hierarchy aidstheoperatortoseparatereleventfromlessreleventinformation byproviding displaysofdifferent levelsofdetail.Acolorcodeshouldhelptheuserseparateimportant fromunimportant information byproviding different levelsoforganization withineachdisplay.1.Reference orbackroundcolor..Thiscolorshouldbeclearlyvisiblebutsubdued.Itshouldnotbethemostsalientcolor(i.e.notthebrightest colorortheonewiththebestcontrast) available ontheCRT.Staticorreference materialshouldmakeupthiscategory.

2.For'eroundcolor.Thiscolorshouldbethemostsalient(brightest, rbestcontrast) coloravailable.

Thiscategoryshouldincludedynamic,important information, information thatisnecessary tofulfillthetasksthedisplayisdesignedtosupport.

3;Hihlihtcolors(upto2colors.Thesecolorsshouldclearlydemandtheuser'sattention forexample,redforalarminformation.

Thiscategoryshouldcontaintheleastnumberofitems,only3or4perpage.Ifthisisexceededthecolorwillnolongerfulfillitsattention gettingfunction.

Thisschemaorganizes theinformation onapageintolayers-almostaddingadepthdimension ontothepage.(Actually perceptual-researchshowsthatfiguresdotendtostandoutondepthinfrontoftheground;Coren,1976).Thepyramidoflayersfocusestheuser'sattention directlyontoimportant (foreground) andcritical(highlighted) information.

Withineachcodinglevel,dispersed information isorganized intoasingleunit.Thisapproachcanbeexpandedtoothercodingtechniques aswell.Forexample,achromatic highlighting techniques couldbeusedand2levelsofbrightness couldrepresent theforeground andreference information levels.Howeverthereshouldbeaceilingof4codinglevels.Thecodingschemepresented herefulfillseachofthecodingfunctions described earlierinasystematic way.Searchperformance isenhancedsinceinformation iscategorized atanoptimumlevel(3or4categories).

Criticalinformation standsoutthroughthepyramidstructure andeachcolorlevelpullstogetherdispersed butrelatedinformation.

Thecodinglevelsaidinformation reduction byorganizing information according toprioritylevels.'inally ittakesadvantaoe oftheuser'sperceptual andattentional mechanisms.

HumanFactorsreconmendations oncodingusuallyprovideanannotated listofeightcolors(theeightcolorsusuallyavailable onCRTsystems).

Eachcolorismatchedasbestsuitedfordifferent typesofinformation.

Nosuchlistisprovidedherebecauseitencourages theoveruseofcolorcodingandbecausetheappropriate colorsforeachapplication shouldbedetermined bytesttrialswiththeactualCRT,displaysandvisualenvironment.

-Interactive Techniues.Codingtechniques arenottheonlymeansavailable tofacilitate operatorprocessing andinterpretati onofcomplexdisplays.Interacti vecapabilities canbeincorporated intothesystemtoenableuserstoseparatereleventfromirrelevent information.

OnsomeCRTsystems,multiplegraphicplanescanbeutilizedfordifferent groupsofinformation sothatanoperatorcansuppressorrequestinformation asrequired.

Gridlines, labels,units,scales,andlimitsareallcandidates forsuppression byanexperienced operator.

Anoperator,

.shouldalsobeabletointeractively requestsupplemental information thatdoesnotwarrantcontinuous display.Forexample,onagraohical display,anoperatorcouldrequestadigitaldisplayofactualorhistorical parameter values.Interactive techniques caribeeffectively usedinadditiontocodingmethodstoreducethedensityofcomplexdisplays.

Table1-Alternative CodingDimensions forCRTApplications Dimension Recomnended NumberofLevelsAlternative Alications Symbology Size10-15maxIdentifydifferent cnmoonents andtheiroperational statusHighlight dynamicvs.staticdataHighlight operational vs.non-operational components Differentiate pipingwithfl'owvs.noflowHighlight moreimportant data,symbols,orlinesDifferentiate monitored vs.non-monitored dataLineStructure Brightness/

Intensity ColorAchromatic Highlighting 3-43-4recom.on/offDifferentiate flowvs.noflowSuppressbackground infoHighlight cautionandwarninginformation Differentiate operatational vs.non-operational components Differentiate pipingwithflowvs.noflowDifferentiate dynamicvs.staticdataHighlight cautionandwa'minginformation Highlight cautionandwarninginformation Differentiate operational vsnon-operational components Candidates forCodinginProcessControlVariousmedia(steam,water...)

Conditions orstates(on/off,running/stopped, open/closed, flow/noflow.available/unavailable)

Controlmodes(manual/automatic, remote/local)

Plantstatus(pre-trip/post-trip, terminate/mitigate)

Information priority(alarms)Background orreference information versusforeground informationDataquality(good/inconsi stent/bad/manually entered)~Information state(normal/cautioning/abnormal)

Therearemanyusefulideasonhowtoapplycodinqtechniques todifferent applications.

Itisnotsufficient tomatchonecodingcandidate toonecodingdimension untilthesetofcandidates isexhausted.

Thisapproachwillguarentee anunsatisfactory codingscheme.Codingquestions mustbeexaminedasanintegrated settogetherwithinformation transferrequirements generated viataskanalysis.

Thisapproachwillpreventconflicts betweenindividual codesanditwillpreventcodingschemeswhichincrease, notreduce,displaycomplexibi1ity.

I1e4j