實施SAP-R3軟件中項目管理

ProjectManagementwithSAPR/3

TeachingMaterialfortheDepartmentof

ProductionManagement

ViennaUniversityofEconomicsand

BusinessAdministration

AndreasMild

AlfredTaudes

TOC\o"1-3"

1 Introduction

3

2 Basics&Keywords

4

3 Gettingreadyfortheworkshop

7

4 CaseStudy

13

4.1 Casedescription

13

4.2 DataforProjectRealization

14

5 Planningtheprojectstructure

15

5.1 General

15

5.2 ImplementationinSAP

17

6 Scheduling

26

6.1 General

26

6.2 Basiccalculations

29

6.3 Implementation

30

6.4 Theprojectplanningboard

41

7 Costplanning&Controlling

47

7.1 General

47

7.2 Implementation

48

8 Lookingupthecosts

61

9 CapacityPlanning

64

9.1 General

64

9.2 ImplementationinSAP

65

10 EarnedValueAnalysis

69

10.1 General

69

10.1.1 Measurementtechniques

69

10.1.2 CalculationofEarned-ValueandDeviationAnalysis

73

10.1.3 Aggregation

74

10.2 Implementation

74

11 Execution

77

11.1 Implementation

77

11.1.1 Confirmingnetworkactivities

77

11.1.2 Invoices

79

11.1.3 Material

83

12 InformationSystem

86

12.1 Implementation

86

12.1.1 Costreports

86

12.1.2 Earned-ValueAnalysis

92

13 Literature

98

Introduction

Thisscriptservesasabasisfortheworkshop"ProjectManagementwithSAPR/3".ThisworkshopispartofaseriesofSAP-relatedworkshopswhichareheldbytheDepartmentofProductionManagementoftheViennaUniversityofEconomicsandBusinessAdministration,headedbyProf.Dr.AlfredTaudes.TheworkshopwasdevelopedbyAndreasMild.

ThegoalofthisProjectManagementWorkshopisthat,afterhavingattendedit,eachstudentshouldbefamiliarwiththetheoreticalbackgroundsandbeabletoplanandcontrolaproject.Theprojectmanagerhasthetaskofensuringthattheprojectisexecutedefficiently,ontime,andwithinthebudget-whichhe/sheachievesbymakingcertainthattherequiredresourcesandfundsareavailablewhenneeded.Everystudentshouldthenbeabletoputhis/herSAPknowledgeintoaction.

Tomakethecontinuousimprovementofthisscriptpossible,pleasereportmistakesfoundorideasforfurtherdevelopmentto.

Basics&Keywords

SAPR/3isanintegratedandindustry-independentstandardsoftwarewhichcovers,integratesandconnectsallfunctionalareasinabusiness.SAPAGdefinesintegrationas"definedcommunication".AFOS(Hrsg.)SAPArbeit,Management.Braunschweig/Wiesbaden1996p.59

AlthoughR/3isdesignedforcompleteintegration,itcanalsobeusedforacoupleofbusinessareas.ComputerweltNo.13of13.3.1998,p.20

SAPistheabbreviationfor“Systeme,Anwendungen,Produkte”,theGermanwordsfor“Systems,Applications,Products”.AFOS(Hrsg.)SAPArbeit,Management.Braunschweig/Wiesbaden1996p.59

Informationaboutthecompanycanbefoundat:.

Projectsaretaskswithspecialcharacteristics.Attributesofaprojectarethefollowingissues:

complexity,non-repetitivity,highrisk

detailedgoalstobeachieved

timerestrictions

highcostandcapitalexpenditure

qualityrequirements

oftenstrategicsignificance

Tobeabletoplan,monitor,control,andcarryoutaprojectasawhole,theprojectgoalsmustbepreciselydescribedandtheactivitiestobeperformedhavetobestructured.

Aprojectcanbedescribedasfollows:

accordingtohowitisorganized,i.e.byexplainingtheprojectstructure,

accordingtotheprocessesinvolved.

Aprojectstartsoutasastatementofworkwhichiseitherawrittendescriptionoftheobjectivestobeachievedandthedesiredroughschedulelikestartandenddates.Inthedescriptiononecouldincludealsoperformancemetricsandbudgetconstraints.

Aprojectisfurthersubdividedintomeaningfulpieces,referredtoastasks.Taskstakeusuallylessthanafewmonths.Thetaskcanbefurthersubdividedintosubtasks.

Aworkpackagecanbedefinedas“agroupofactivitiescombinedtobeassignabletoasingleorganizationalunit.”ChaseR./AquilanoN./JacobsR.ProductionandOperationsManagement:ManufacturingandServices,p.48

Theprojecttasks,subtasks,andworkpackagesarebroughtintoahierarchybydefiningaworkbreakdownstructure.

Theindividualelementsrepresentactivitieswithintheworkbreakdownstructureandarecalledworkbreakdownstructureelements(WBSelements).

WBSelementscanbe:

tasks

partialtaskswhicharesubdividedfurther

workpackages

WBScanbestructuredaccordingto

object

function

phase

Whichkindofstructuringisuseddependsonthefocusoftheproject.Objectsorientationisoftenused,ifthemainpartoftheprojectisaphysicalobjectlikeapowerplant.Functionalorganisationispreferred,ifmanydifferentpartsofanorganisationormanyorganisationsareinvolved.

Inpractice,allthreekindsofstructuringareusedwithinoneWBS.

“ProjectManagementcanbedefinedasplanning,directing,andcontrollingresources(people,equipment,material)tomeetthetechnical,costandtimeconstraintsoftheproject.”ChaseR./AquilanoN./JacobsR.ProductionandOperationsManagement:ManufacturingandServices,p.48

Theprimaryreasonwhyprojectsfailisinsufficienteffortintheplanningphase.ChaseR./AquilanoN./JacobsR.ProductionandOperationsManagement:ManufacturingandServicesp.69

ProjectManagementthusisconsideredasveryimportant.

TheSAPProjectSystemenablescloseandconstantmonitoringofallaspectsofaprojectbyhavingconstantaccesstodatainallthedepartmentsinvolved.

Projectmanagementcanbesubdividedintoprojectplanning,i.e.thetaskwhichwillbeundertakenbeforetheprojectstarts,andprojectcontrollingduringtheimplementationoftheproject.Planningmustinclude:

organization–service

process–dates

costs

capacity

Therearemanypossibleprojectgoalssuchas,forexample,torealizeapositivenetpresentvalue,toachieveahighimputedinterest,tominimizecosts,tocovercosts,tomaximizegrossprofit,orsimplytofinishasearlyaspossible.However,itisimportant,thatgoalsaredefinedoperationally,thaitiswhenitispossibletomeasuretowhichextentthegoalhasbeenachieved.

Theprojectmanagerbreakstheprojectdownintoasetofactivities.Thenhealsodefinestherelationshipsamongtheseactivities.Theoutcomeisaguidelineregardingtheactivitiesthatcanbeperformedinparallelandthosethathavetobedoneinasequentialorder.Thistaskisdoneviaplanningbynetwork.

Now,thereareactivitiesthatrequirecapacitiesandresourceslikepersonnelandmaterial.Suchresourcesarelimitedandtheserequirementshavetobeconsideredinordertobeabletodevelopafeasible,soundplan.Informationfromothermodulesase.g.thematerialplanningmoduleisrequired.

Thesystemcalculatesthematerialrequirementsforeachstepoftheprojectandorganizesthatmaterialsareboughtintimetoavoiddelays.Whenpurchasingmaterial,thesystemtakesintoaccountordersizes,inventorypoliciesaswellasotherinformation.

Topreparethefinancialstatements,thevalueofworkinprogress(includingprojectwork)hastobecalculated.ThisalsorequiresinteractionofsomeR/3modules.

Thus,thesystemneedsinformationfromallbusinessareassimultaneously.Andthisisexactlywhatintegrationdoes.

TheprojectmoduleispartoftheintegratedconceptofSAPR/3providinginterfacestoothermoduleslikeAccounting,Distribution,MaterialManagementandProductionPlanningandControl.Eachareawithintheorganizationhasitsownstructureanditsownviewoftheproject,butdatahastobeenteredonlyonce.

Gettingreadyfortheworkshop

Thischapterprovidesinformationonthefirstuseofthesystem.

LoggingonR/3

Loggingoff

SAPR/3isaclient/serverapplication.Therefore,youhavetocanceltheconnectionwiththeserverbytellingitthatyouwanttologoff.

CreateSession

Oftenitisusefultoopenmorescreens.Youcandothisbycreatinganewsession,likeanewdocumentinawordprocessor.

SAPHelp

Ifyouwanttogetsomebasicinformationaboutaspecificfield,focusthisfieldwithyourmouseandpress<F1>.Thedialogboxindicateswhatthefieldisfor.Sometimesevendependenciesareexplained.

Matchcodes

Matchcodesareusefulforfindingdata,becauseitisdifficulttoknow/remembertheidentificationnumberofalinepositionsuchasamaterial.

Example:

Youwanttoeditthematerialmasterofamaterial.Youdon’tknowthenumber,butyouknowthatthematerialdescriptionstartswithsomethinglike“PM_”

IfyoupressF4yougetasearch-maskwhereyouareabletosearchwithwildcards

AfterhavingpressedEnteryougetalistwiththesearchresults.

Thenyoucanselectonematerial,youcansortorcancel.

TransactionCodes

Thefollowingscreenwillbeoftenusedduringtheworkshop.Thus,wecanuseTransactionCodesforfasteraccess.

ThenselectStructureplanning–ChangeProject.

Now,wewantto“bookmark”thisscreen.

So,welookupthetransactioncode.

Thestatusdialogboxopens:

Hereweseealotofinformationconcerningimportantrelevanttechnicaldetails.

Whereveryoufindyourselfinthesystem,youcangettothisscreenbyenteringCJ20intheTransactionscreen.

Letusrefinethisalittlebit.Ifyouhaveseveraltransactioncodes,youmaygetconfused.Keyintheappropriatetransactioncodeandthecommenteditprojectstructure.

Then,ifyouopenthecomboboxofthetransactioncodesafterhavingenteredmorecodes,youwillfindtheappropriateone.

TheStandardToolbar

Inmanyscreensyouwillfindthestandardtoolbar.

Savebutton

Whenyoupressthesavebutton,thesystemalsovalidatesyourinput.Iftherewasanerror,youhavetocorrecttheerrorfirst,beforeyoucanproceed.

Backbutton

Ifyouclickthebackbuttonyoureturntothepreviousscreenwithoutsavingyourdata.

Help

Enterbutton

Whenyouhavefinishedenteringinformationonascreen,youpresstheEnterbuttonwhichperformsthesamefunctionaspressingtheEnterkey.

Exitbutton

Pressit,ifyouwanttoleavethecurrentapplicationtogobacktothepreviousmenue.

Cancelbutton

Clickonthisbuttontoexitthecurrenttaskwithoutsaving.TheCancelbuttonperformsthesamefunctionasCancelintheEditmenu.

Printbutton

Pagingkeys

Find/Findnextbutton

Clickonthisbutton,ifyouwanttoperformasearchfordatarequiredinthescreenyouarecurrentlyworkingin.

CaseStudy

Casedescription

ThiscasewasdevelopedinordertodemonstratetheprojectsystemofSAPR/3.Allpricesanddataarepurefictionandheldverysimple.

Theobjectoftheprojectisthespecificationandinstallationofanelevator.

Physically,theElevatorconsistsof

acabine

anengine

mechanicalparts

acontrolunit

Inthecourseoftheproject,thesepartsmustbeconstructed,procuredandassembled.

Attheend,anexternalinspectionoftheentiresystemisprescribed.

Theprojectmustbefinishedby30.6.2023.

Thecompanyconsistsoftwoworkcenters:

Development(PROJ-RD)

Installation(PROJ-INS)

SpecificationactivitiesareperformedbytheDevelopmentdepartment.Procurementactivitieswillbedoneoutsidetheprojectorganisation,andneithercostnorcapacityconsiderationsareplannedwithinaprojectforprocurement.InstallationisdonebytheInstallationdepartment.

Inparticular,theactivitiesareasfollows:

Activity

Duration

Work

Work-center

Specificationofthecabine

10

20

Development

Specificationoftheengine

10

10

Development

Specificationofmechanicalparts

20

10

Development

Specificationofthecontrolunit

2

10

Development

Procurementofthecabine

20

Procurementoftheengine

50

Procurementofmechanicalparts

10

Procurementofthecontrolunit

10

InstallationI

15

100

Installation

InstallationII

20

100

Installation

ExternalInspection

1

external,80.000

Specificationactivitiescanbeperformedinaconsecutiveorderonly.Specificationstartswiththecabine.Aftercompletion,thespecificationoftheenginecanbedone.Then,themechanicalpartscanbedesigned.Thelastactivityisthedesignofthecontrolunit.

Afterthecompletionofeachspecificationactivity,theprocurementofthespecificitemcanbeeffected.

AftertheprocurementofallpartstheInstallationcanstartandmustbedoneintwoconsecutivesteps(I+II).

Thefinalactivityoftheprojectisexternalinspection.

A10%planningreserveonthebaisisofplannedcostisrequired.NoactualcostshouldbepostedtothisWBSelement.

Correspondingmaterialsassignedtothepurchasingactivities

ParametersfürEarned-ValueAnalysis

AllspecificationactivitiesandInstallationIIusethe20-80Methodforperformancemeasurement.Procurementactivitiesuse0–100method.

InstallationIhas3milestones,viz.Preparationfinished(20%),Installationfinished(80%),Qualitychecked(100%).

DataforProjectRealization

Activity

Start

End

Work

Specificationofthecabine

20

Specificationoftheengine

30

Specificationofmechanicalparts

20

Specificationofthecontrolunit

Procurementofthecabine

Procurementoftheengine

Procurementofmechanicalparts

Procurementofthecontrolunit

InstallationI

InstallationII

ExternalInspection

Externalinspectionhadtobepaidinadvanceat3.2.2023(100000ATS).

Allmaterialwastakenfromstockatgiventime.

Planningtheprojectstructure

General

Eachprojectstartswiththedefinitionandclassificationofthestructuresrequiredforprocessingandtheincorporationoftheseintotheexistingenterprisestructure.

TheProjectSystemhasnoorganizationalstructuresofitsown;ithastobeincorporatedintotheexistingstructurebymakingassignmentstotheorganizationalunitsinAccountingandLogistics.SAPOnlineDocumentationIDESRelease4.0B

Afterthat,theprojectisbrokendownintomeaningfulpiecesinahierarchyreachingfromtaskstothelowestlevel,theworkpackages.

DatastructureinSAP

Asmentionedabove,theprojectmustbeincorporatedintotheexistingstructurebyassigningorganizationalunitsinAccountingandLogistics.

Source:SAPOnlineDocumentationIDESRelease4.0B

Thischartprovidesanoverviewofwhatcanbeassignedtoaprojectanditscomponents.WewilldefinetheSAPvocabularylateron.

Thework-breakdown-structure(WBS)definesthehierarchyofthetaskswithinaprojectanddividestheprojectintousefulsteps.

TocontrolcostsassignedtoWBSelements,operativeindicatorsareused.

ThefollowingoperativeindicatorscanbeassignedtoaWBSelement:

Planning

WBSelementsforwhichcostscanbeplanned

Accountassignment

WBSelementstowhichcostscanbeassigned

Billing

WBSelementstowhichrevenuescanbeposted

ImplementationinSAP

Inthissectionwecreateanewproject.Wethenwillhavealookatthecontrolparameters.Afterthatweentertheworkbreakdownstructure.Finally,thestatusconceptofSAPR/3willbeexplained.

Createnewproject

Thus,wegettotheinitialscreen:

Weenterourprojectdefinition,adescriptionofourprojectandselectthestandardprofileforprojects.

Inourcase,weonlysetafinishdate.WhenpressingEnter,awarningmessagethatthisdateisnotaworkingdaymightoccur.OnecanpassthewarningbypressingEnter

Wethensaveourworkandgettheconfirmationthattheprojecthasbeencreated.

Note:Itiswisetosaveyourworkfromtimetotime.Wewillnotmentionthesaveprocedureintherestofthemanuscript!

Tocontinue,wehavetochoosetochangeourproject.

Makesurethatthecheckboxwithactivitiesisalwayschecked.Clickexecutetoproceed.

Nowhehavecreatedanewproject.AlthoughwehavenotkeyedinanydataexcepttheProjectProfileNumber,manyparametershavealreadybeenassignedtoournewproject.

Generalcontrolparameters

Clickheretoviewtheglobalparameters.Thissectionshouldprovideyouwithabasicinsightintowhichparametersareset.IfyoufeelthattheresultscalculatedbyR/3arenotlogical,youshouldhaveanideawheretostartsearchingtherelevantcustomizingdetails.

TheprojectprofilespecifiesgeneraldatalikeControllingarea,Plant,Factorycalendar,Planningmethodetc.Whencreatingtheproject,theprofileischoosen.

Thenetworkprofilespecifiesgeneraldatalikesettingsforthegraphicalrepresentation,activityparameters,likethecurrencydefaultofexternallyprocessedactivities.

IntheWBSschedulingprofileitemsliketheschedulingtype(forward,backward)arespecified.

Thebudgetprofilespecifiesitemslikebudgetingcurrency,thevalidtimehorizonforbudgetingbackin-tothepastorintothefuture

Theplanningprofilespecifies,e.g.,costingvariantandtimehorizon.

Planningparameters

Inthegeneralparametersection,manyparametersaresetasdiscussedabove.Naturally,onecanoverrideapartoftheminthecurrentproject.However,wearenotchanginganyparameters.

Hereyoucanspecifyifyouwanttousetop-Down,bottomup,oropenplanning.

Herewespecifywhatthesystemshoulddoifschedulingdeterminesdateswhicharenotwithinthebasicdates.Incase,thescheduleddatesshouldbetakenoverasnewdates.

Animportantparameteristheschedulingtype.Hereyouspecify,ifyouwanttouseforward,backwardorotherschedulingtypes.

Startenteringthedatagiveninthescreenshotbelow.Ifyouarefinished,pressEnter.

Then,yourscreenshouldlooklikethis:

Levelingup/downWBSElements

Thereisamistake.WBSElementELV_000-300shouldhavelevel2.

SelecttheWBSElementtolevelingitdown.

InsertingWBSElements/activities

WehaveforgottentoenterenterActivity203,ProcurementofthemechanicalpartsandActivity204,Procurementofthecabine.

SelecttherowabovewhichyouwanttoinsertarowandadditbymenueorsimplybypressingF6.Proceedwiththesecondrowinthesameway.Donotforgetthattheseactivitiesdonothavealevel.

Afterthesechangesyourscreenshouldlooklikethis:

The“hidden-quick-menue”

Ifyoupresstherightmousebutton,yougetalistofusefulcommands.Allthesecommandscanalsobeaccessedviamenuesandbuttons.However,youarefasterwhenyouusetheright-mouse-quick-menue.

UserStatusandBusinessAdministrationProcedures

Astatusdocumentsthecurrentstateofprocessingofanobject.Dependingonwhichbusinesstransactionisperformedforanobject,suchasaWBSelement,aninternalorder,oranetwork,thestatusofthatobjectchanges.Thestatusofanobject,inturn,influenceswhichbusinesstransactionscanbecarriedoutforanobject.

Therearetwotypesofstatuses:

Theuserstatusandthesystemstatus.

Asystemstatusissetbythesystemwhichtellsusthataparticularfunctionhasbeencarriedoutforanobject.Ausercannotdelete,change,orotherwiseamendthesystemstatusinanyway.

Auserstatusisastatuswhichcanbesetbytheuserinadditiontothecurrentsystemstatus.Inthisworkshop,wewillskiptheuserstatusandfocusonlyonthesystemstatus.

Now,thesystemstatusoftheprojectisCREATED.

Ifyouwanttocheckthisbyyourself,pressCRTL+F9fromtheprojectstructurechangingscreenandclicktoBusinessTransactions.Nowwegetalistofwhichbusinessproceduresarecurrentlyallowedandwhicharecurrentlydisabled.

Anumberofbusinesstransactionsarecurrentlydisallowed.Inordertoallowforenteringactualdata(e.g.viaIncominginvoices),wemustchangetheuserstatus.

Forthispurpose,wearegoingtoreleasethewholeproject.Selectallrowsandreleasetheproject.

Yougetthemessagethatthestatuswaschanged.

Confirmit.

Now,checkifwearecurrentlyallowedtoreportcosts.SelectthehighestWBSElementandthenpressCRTL+F9

ClicktoBusinessTransactionstoseewhathaschanged.

NotethatnowwearenolongerallowedtodeleteWBS-Elements.

PressEnterandleavethestatusscreenbygoingback.

Beforereleasingtheprojectwehadalreadyselectedallactivities.Thuswehavereleasedthewholeproject.NotethatwewouldhavebeenabletoselectonlyafewactivitiesorWBSelements.Therefore,itispossiblethatdifferentWBSelementsanddifferentactivitiescanhaveadifferentstatus.Infact,inpracticethisisthecasewithlarge-scaleprojects.

OperativeStructures

GetintothescreenchangestructureplanningbyusingTransactioncode“CJ20”andselectWBSbasicdata.

Checktheboxes“PE”and“Acct”totoallowforplannedcostsandforactualcosts.Notethatispossibleandsometimesusefultoallowforplannedcostonanaggregatelevel,butnotforactualcost.

Scheduling

General

Intop-downplanning,westartatthehighestleveloftheworkbreakdownstructure(WBS),andallthesubordinateWBSelementmustfallwithinthetimeframeoftheparticularhigherWBSelements.Incontrast,inbottomupplanning,westartatthesubordinatelevelsandaggregatetheplantothetop.Planningwithouthierarchicaldependenciesisreferredtoasopenplanning.However,severalconstraintshavetobeconsidered.Forexample,wecouldspecifythatthemanufacturingprocessmustendbeforetheannualplantshutdown.Apowerfultoolinprojectmanagementisplanningbynetwork.

Asapreliminarysteptogetaroughideaaboutthetimestructureofaproject,GANTTChartsareused.Thissimplymeansthatthedurationofeachactivityisdrawnagainsttime.Theproblemisthatfunctionalrelationshipsamongsequentialactivitiesarenotcapturedformallyandchangesrequireanewdrawing.Inanetworkthereisusuallyareasonforaspecificsequenceofactivities.Forexample,theremaybetechnicaldependenciesbetweenindividualactivities.

Exampleofanetwork.Source:SAPDocumentationCD

Inordertoconsidertheserelationships,severalalgorithmsforplanningproblemshavebeendevelopedandarereferredtoinanumbrelladefinitionasplanningbynetwork.

Theessentialcomponentsofanetworkare:

Activities

Relationships

Activitiescanbeseenas"componentsofaprocess"withthefollowingcharacteristics:

Theytakeacertainperiodsoftime

Theyhaveadefinedstartandadefinedend

Theyareprocessedwithoutinterruption

Resourcesareneededtoexecutethem

Theyinvolvecosts

DifferentkindsofnetworktypeshaveemergedinthefieldofOperationsResearch.Startingwithdeterministicdurationsandstructure,networkswithstochasticdurations(likePERT)andevenstochasticstructure(likeGERT)offerpowerfultimeplanningtechniques.However,practitionersarescepticalabouttheresults,andlarge,complicatedprojectstructuresrequiretoolswhicharerathereasytohandle.Therefore,wewillonlydiscussMetraPotentialMethod(MPM)whichisusedinthePSmodulaswell.MPMmethodusesdeterministicdurationsandstructures.Asaconsequence,neitherprobabiltiesof,e.g.,aspecificdurationoftheprojectcanbecalculatednorcanbecapturedaprojectstructurewhichhasstochasticelements.Thiswouldbethecase,e.g.,ifwewishedtomodelasituationatestcouldbepassedwithacertainprobability.ThiswouldleadtoalooponaMPMstructurewhichisforbidden.

Anetworkdoesnotonlygraphicallydisplaytherelationshipsamongvariousactivities,itprovidesalsoinformationonthecriticalpath.Thecriticalpathindicateswhichactivitiesarethemostcriticaltobeperformedintimetoavoiddelayingthewholeproject.Higgins,James:TheManagementChallengep.232

PlanningbynetworkisbasedontheTheoryofGraphs.Heinrich,Lutz:Systemplanungp.206

MPMusesnodestorepresentactivitiesandarrowsfortheirrelationshipsasthisiseasiertofollow.OnemustknowthatSAPsupportsseveraltypesofrelationshipsandnotonlythestandardrelationship.Thefollowingrelationshipsaresupported:

Finish-Start

Theprecedingactivitymustfinishbeforethefollowingactivitymaystart.

Start-Start

Oneactivitycannotstartuntiltheotheronehasstarted.

Finish-Finish

Oneactivitycannotbefinisheduntiltheotheroneisfinished.

Start-Finish

Oneactivitycannotbefinisheduntiltheotheronehasstarted

Forsomeactivities,theearliestpossiblestartandthelatestpossiblestartdiffers.Thedifferencebetweentheearliestpossiblestartandthelatestpossiblestartiscalledslacktime.Aslacktimegreaterthanzeromeansthatthedurationoftheactivitycanbelongerthanplannedwithoutdelayingthecompletiondateofthewholeproject.Thesequencesofactivitieshavingaslacktimeofzeroarecalledthecriticalpath.Inthiscontextcriticalmeansthat,ifthedurationofoneoftheseactivitiesislongerthanexpected,thecompletiondateofthewholeprojectisdelayedbyatleastthatperiodoftime.Onemustalsorealizethattherecanbeseveralcriticalpaths.Moreover,thecriticalpathscanchangeduringtheprojectasaresultofunexpecteddelaysofcertainactivities.

ThechangeofthecriticalpathduetoexcessiveconsumptionoftheslacktimeisreferredtoasParkinsonPhenomena.Schierenbeck,Henner.EinführungindieAllgemeineBetriebswirtschaftslehre,p.165

Theslacktimeforanactivitycannotbeusedwithoutaffectingtheslacktimeforotheractivities.Asaruleofthumb,thetotalslacktimecanbeusedonlyoncewithinanon-criticalpathwithoutchangingtheparticularpathintoacriticalone.Thus,theMPM(MetraPotentialMethod)methodsplitstheslacktimeintofourdifferentparts.Schierenbeck,Henner.EinführungindieAllgemeineBetriebswirtschaftslehre,p.159ff

Thetotalslacktimeiscalculatedasthedifferencebetweentheearliestpossiblestartandearliestpossibleend.Thisisequaltothedifferencebetweenthelatestpossiblestartandthelatestpossibleend.

Thefreeslacktimeattheendiscalculatedassumingthatallpredecessorshavebegunattheearliestpossibledate.Thus,thefreeslacktimeattheendcalculates,providedtheassumptionholds,thetimetheactivitycanb