Critical Path Analysis & PERT Charts (taken from Planning and scheduling more complex projectsCritical Path Analysis and PERT are powerful tools that help you to schedule and managecomplex projects. They were developed in the 1950s to control large defense projects, and havebeen used routinely since then.As with Gantt Charts, Critical Path Analysis (CPA) helps you to lay out all tasks that must becompleted as part of a project. They act as the basis both for preparation of a schedule, and ofresource planning. During management of a project, they allow you to monitor achievement ofproject goals. They help you to see where remedial action needs to be taken to get a project backon course.The benefit of using CPA over Gantt Charts is that Critical Path Analysis formally identifies taskswhich must be completed on time for the whole project to be completed on time, and alsoidentifies which tasks can be delayed for a while if resource needs to be reallocated to catch upon missed tasks. The disadvantage of CPA is that the relation of tasks to time is not asimmediately obvious as with Gantt Charts. This can make them more difficult to understand forsomeone who is not familiar with the technique.A further benefit of Critical Path Analysis is that it helps you to identify the minimum length of timeneeded to complete a project. Where you need to run an accelerated project, it helps you toidentify which project steps you should accelerate to complete the project within the availabletime. This helps you to minimize cost while still achieving your objective.How to use the tool:As with Gantt Charts, the essential concept behind Critical Path Analysis is that you cannot startsome activities until others are finished. These activities need to be completed in a sequence,with each stage being more-or-less completed before the next stage can begin. These are'sequential' activities.Other activities are not dependent on completion of any other tasks. You can do these at any timebefore or after a particular stage is reached. These are non-dependent or 'parallel' tasks.Drawing a Critical Path Analysis ChartUse the following steps to draw a CPA Chart:1.ListallactivitiesintheplanFor each activity, show the earliest start date, estimated length of time it will take, and whether itis parallel or sequential. If tasks are sequential, show which stage they depend on.For the project example used here, you will end up with the same task list as explained in thearticle on Gantt Charts (we will use the same example as with Gantt Charts to compare the twotechniques). The chart is repeated in figure 1 uterprojectNB: The start week shows when resources become available. Whether a task is parallel orsequential depends largely on context.

TaskPossiblestartLengthType1. High level analysisweek 15 dayssequential2. Selection of hardware platformweek 11 daysequential13. Installation and commissioning ofhardwareweek 32 weeksparallel24. Detailed analysis of core modulesweek 12 weekssequential15. Detailed analysis of supporting utilities week 12 weekssequential46. Programming of core modulesweek 43 weekssequential47. Programming of supporting modulesweek 43 weekssequential58. Quality assurance of core modulesweek 51 weeksequential69. Quality assurance of supportingmodulesweek 51 weeksequential710.Core module trainingweek 71 dayparallel611.Development of accounting reporting week 61 weekparallel512.Development of managementreportingweek 61 weekparallel513.Development of managementanalysisweek 62 weekssequential514.Detailed trainingweek 71 weeksequential1-1315.Documentationweek 42 al Path Analyses are presented using circle and arrow diagrams.Dependenton.13arrowdiagramIn these, circles show events within the project, such as the start and finish of tasks. Circles arenormally numbered to allow you to identify them.An arrow running between two event circles shows the activity needed to complete that task. Adescription of the task is written underneath the arrow. The length of the task is shown above it.By convention, all arrows run left to right.An example of a very simple diagram is shown below:

This shows the start event (circle 1), and the completion of the 'High Level Analysis' task (circle2). The arrow between them shows the activity of carrying out the High Level Analysis. Thisactivity should take 1 week.Where one activity cannot start until another has been completed, we start the arrow for thedependent activity at the completion event circle of the previous activity. An example of this isshown below:Here the activities of 'Selecting Hardware' and 'Core Module Analysis' cannot be started until'High Level Analysis' has been completed. This diagram also brings out a number of otherimportant points: Within Critical Path Analysis, we refer to activities by the numbers in the circles at eachend. For example, the task 'Core Module Analysis' would be called 'activity 2 to 3'. 'SelectHardware' would be 'activity 2 to 4'.Activities are not drawn to scale. In the diagram above, activities are 1 week long, 2weeks long, and 1 day long. Arrows in this case are all the same length.In the example above, you can see numbers above the circles. These show the earliestpossible time that this stage in the project will be reached. Here units are whole weeks.A different case is shown below:

Here activity 6 to 7 cannot start until the other three activities (12 to 6, 5 to 6 and 9 to 6) havebeen completed.See figure 5 for the full circle and arrow diagram for the computer project we are using as anexample.Click here to see the full Critical Path DiagramThis shows all the activities that will take place as part of the project. Notice that each event circlehas a figure below it as well as a figure above. This shows the latest time that it can be reachedwith the project still being completed in the minimum time possible. You can calculate this bystarting at the last event (in this case number 7), and working backwards.You can see that event 4 can be completed any time between 1.2 weeks in and 7.8 weeks in.The timing of this event is not critical. Events 1 to 2, 2 to 3, 3 to 4, 4 to 5, 5 to 6 and 6 to 7 mustbe started and completed on time if the project is to be completed in 10 weeks. This is the 'criticalpath' - these activities must be very closely managed to ensure that activities are completed ontime. If jobs on the critical path slip, immediate action should be taken to get the project back onschedule. Otherwise completion of the whole project will slip.'CrashAction'You may find that you need to complete a project earlier than your Critical Path Analysis says ispossible. In this case you need to take action to reduce the length of time spent on project stages.You could pile resources into every project activity to bring down time spent on each. This wouldprobably consume huge additional resources.A more efficient way of doing this would be to look only at activities on the critical path.

As an example, it may be necessary to complete the computer project in figure 5 in 8 weeksrather than 10 weeks. In this case you could look at using two analysts in steps '2 to 3' and '3 to4', and two programmers instead of one in step '4 to 5'. This would shorten the project by twoweeks, but would raise the project cost - doubling resources at any stage often only improvesproductivity by, say, 50%. This occurs as time spent on coordinating the project consumes timegained by increasing resource.Note that in this example, shortening the project by two weeks would bring activities '3 to 11', '11to 12' and '12 to 6' onto the critical path as well.As with Gantt Charts, in practice project managers tend to use software tools like MicrosoftProject to create CPA Charts. Not only do these ease make them easier to draw, they also makemodification of plans easier and provide facilities for monitoring progress against plans. MicrosoftProject is reviewed at the top of our left hand title bar.PERTPERT stands for Program Evaluation and Review Technique.PERT is a variation on Critical Path Analysis that takes a slightly more skeptical view of timeestimates made for each project stage. To use it, estimate the shortest possible time each activitywill take, the most likely length of time, and the longest time that might be taken if the activitytakes longer than expected.Use the formula below to calculate the time to use for each project stage:shortest time 4 x likely time longest ------------6This helps to bias time estimates away from the unrealistically short time-scales normallyassumed.Key points:Critical Path Analysis is an effective and powerful method of assessing: What tasks must be carried outWhere parallel activity can be performedThe shortest time in which you can complete a projectResources needed to execute a projectThe sequence of activities, scheduling and timings involvedTask prioritiesThe most efficient way of shortening time on urgent projects.An effective Critical Path Analysis can make the difference between success and failure oncomplex projects. It can be very useful for assessing the importance of problems faced during theimplementation of the plan.PERT is a variant of Critical Path Analysis that takes a more skeptical view of the time needed tocomplete each project stage.

Microsoft Project is reviewed at the top of our left hand title bar. PERT PERT stands for Program Evaluation and Review Technique. PERT is a variation on Critical Path Analysis that takes a slightly more skeptical view of time estimates made for each project stage. To use it, estimate the shortest possible time each activity