Pert Charts for Fun and Profit

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Three kinds of schedules are normally encountered by project managers:  personnel, performance, and financial. Performance schedules are usually constrained by their beginning and ending dates for each task, and provide the general structure for rest of the project’s schedules.  Financial schedules handle the distribution and budgeting of financial resources for those performance tasks over time.  This cost schedule is one of the major drivers of the overall project budget.

The project manager needs to view everything holistically as each of these schedules interrelate.  Project Managers use PERT and Gantt charts to help schedule the tasks within the project.  They can additionally be used to convey progress and plans with the end customer and team members.  The Project Manager needs to decompose the work into smaller chunks, generally called task decomposition, before any of these tools can be leveraged for scheduling.  The customer also needs to provide their insight into the schedule and deadlines as well, as they will understand interim dates and priorities far better than a project manager unfamiliar with their business. Even though these charts aren’t a cure-all for every project dilemma, these are certainly some of the best tools for project scheduling a project manager can get their hands on.

Pert Chart

The Program Evaluation and Review Technique (PERT) was designed in the 1950’s. PERT has always been an event-driven scheduling technique.   On a PERT chart, the labels are placed on the nodes within the project diagram.

They have generally found uses in aerospace and R & D projects since those projects deal with a great deal of uncertainty for each activity. PERT leveraged an aspect of its predecessor, the critical path method (CPM), another activity-oriented scheduling tool, which placed the activity label on the arrow from node to node in the PERT diagram.  This allowed the the manager to get a scheduled duration for each activity in the chart.  Today, most PERT systems are hybridized, leveraging the best of both the PERT and CPM worlds at the manager’s command. A PERT chart looks like a lot of boxes connected by arrows, basically, is more like flow diagrams to the naked eye.

Gantt Chart

Schedules at the task level generally use a time-driven linear layout or bar chart. The Gantt chart does just this. If you need to show the time-phased requirements for tasks and workers across an entire project, then a Gantt chart is the perfect choice to convey these.  Gantt charts are similar to the PERT/CPM hybrids, but that are far simpler for a team to understand since they make the project’s critical path and milestones so plainly visible.

Understanding what a Gantt chart does, is critical to is effective use.  Take Microsoft Project’s Gantt chart tool, for example.  If you understand the work breakdown of your project and the schedule of each of the tasks therein, you can take advantage of this tool to show the way the project should proceed, when the milestones are expected to be attained, and then you put the Gantt chart together to paint that picture.  You can also use Excel to make this kind of chart by using the stacked bar chart type feature or conditional formatting.  Given that there are so many other very effective project management tools on the market today capable of making Gantt charts with ease, using excel is seldom the best bet.  Regardless of which software you use, you will need to know exactly what your activities are for the project, and which activities hinge on others getting done.  You will essentially put together the timeline for the critical path items and those which are inflexible for whatever reason, and backfill until everything occurs in the order in which you need it to for the project to get finished on time.

In spite of the best laid plans, frequently project overruns occur. At that time whatever scheduling tools are used must be adjusted. It takes human intelligence to make it all work, no matter how sophisticated the software.

Even with the help of charts, it is really up to the Project Manager to understand the flow of work for the project. The best software is only as good as the mind that uses it.

History of the PERT Chart

When managing projects which leverage expensive resources, any project manager who’s any good tries to effectively utilize those resources as best possible.  At the same, the PM strives to complete the project on schedule. Thinkers and innovators throughout the world have been put in a great deal of effort to devise tools to make their work simpler and more easily communicated, rather than the constant rushing against deadlines and inefficient utilization of resources that one frequently finds themselves going through.

The PERT chart is one such tool. Developed by the US Navy in the late 1950s, long after the advent of the Gantt Chart, PERT is an acronym for Program Evaluation and Review Technique. Thousands of contractors and agencies worked with the project managers had to handle for the development of the Polaris Missile. Projects of such mammoth sizes had no precedent in the history of man. There was no prior project management experience available to the managers to handle them. Ingenuity, coupled with determination to succeed against such odds gave rise to a clutch of management tools - all using the humble paper and pencil. At this time, the PERT chart was created.

Charting Basics - How to

A PERT Chart is a visual tool that project management uses to schedule, organize, and coordinate activities of their project. In every project, a list of tasks is broken down (cf: Work Breakdown Structure), to complete in a definite sequence, which define the project. Resources required to complete each task - in terms of money, material, and manpower - are listed.

Tasks are then sequenced one after another along a timeline. Tasks which can be done simultaneously, without having to depend on one another for completion, are noted. Milestones are penned down, which have to be reached while within the project. Creating a PERT chart then involves thinking through the project flow.

The project manager creates circles or rectangles to represent events - or milestones - in the project. These are called Nodes of the PERT chart. Activities which must occur in order to reach a milestone are represented by arrows, and these are known as vectors in PERT terminology. Nodes are linked by the Vectors, and the direction of the Vectors indicates the sequence of activities. Together, the Nodes and the Vectors, along with the information that they carry, form the Chart or the Network Diagram.

The first activity, or set of activities originates the Initiation Node. When multiple activities begin in parallel, the vectors are shown as emanating from the Node, outward. On each Vector is noted the following information:

• Name of the activity that the Vector represents; or some similar identifier
• Expected duration of the activity (in terms of days, weeks, months)
• Number of people assigned to the activity
• Initials of the person responsible for the activity.

Every activity ultimately results in some event or milestone. Correspondingly, every Vector ultimately terminates in some Node. The progression of cause-and-effect; that is, of activities as Vectors ending in events as Nodes continues; until we have a complete chart, wherein all the final activities converge at the completion Node.

There would be some Vectors that do not require any resources. They start from one Node and terminate into another, in order not to break the flow of the network, and to ensure that the entire diagram has just one Node - the completion Node - which has no Node leaving it. These are called Dummy Vectors. (Otherwise there would be “hanging” nodes - events that seemingly have got nothing to do with the project completion!)

Thus, a PERT chart affords the project management a bird’s-eye-view of the entire project. Along with an associated Gantt chart, they are able to gauge where they stand in terms of the project being completed within the estimated time.

Hidden Details

It is not unusual conduct periodic reviews during a project, or after every predefined set of milestones are reached. These review points may be given their place of honor in the PERT diagram, by representing them with a Node, and having all preceding milestone nodes connect to them with the help of dummy Vectors. Progress Reviews may take anywhere between 1 day to 2 weeks or even longer. A prudent project manager has to build in this time consciously in their plan.

Also, frequently, mundane tasks such as documentation, project report writing, and report reproduction are taken for granted. Managers diligent about the slightest schedule slippage must give these activities their deserved place in the PERT chart. This also helps in underlining the importance of such tasks to people who are supposed to carry them out.

Critical Path Management (CPM)

One of the best advantages of creating a PERT chart during project planning is the insight it provides on the Critical Path. In our network diagram above, a critical path is the longest path traversed from the starting Node to the ending Node, in terms of the total of the calendar time taken to achieve each intermediate Node. All activities on this Critical Path must be completed on schedule for the project to finish on time. Seen in this light, each activity in the Critical Path is a critical activity, to be given the utmost attention.  Resources from tasks which are not critical can be reallocated to assist Critical Path elements should issues arise, or inevitably unforeseen conditions occur.  The process of managing the critical path is is referred to as Critical Path Management, or CPM.

On the other hand, an activity outside of the critical path “can” be delayed without the project getting delayed - for a certain amount of time. PERT experts call this the Slack Time for that particular activity.

Sometimes, the Critical Path is not immediately obvious when viewing the Chart cursorily. In such situations, we can determine the following four parameters associated with each activity:

• TES (Task Early Start) - the earliest start time of that activity. Working forward through the network (from start to finish), and keeping in mind the predecessor activities, the earliest time at which an activity can start.
• TLS (Task Late Start) - this is the latest time that the activity in question can begin. This value is arrived at by working backward through the network (from finish to the start), and keeping in mind the deadline for the project.
• TEF (Task Early Finish) - the earliest finishing time of the activity. Usually, this is arrived at keeping in mind optimistic conditions.
• TLF (Task Late Finish) - this is the latest time that the activity can end. Again, optimistic conditions are borne in mind while calculating this value.

Slack for each activity is then computed by subtracting TEF from TLF. The slack thus calculated may be noted on each Vector in the network diagram. The critical path shall then be a path that traverses the diagram across those Vectors where slack is Zero.

Charting Project Progress

After the project plan is created, a thorough PERT chart is in place, customer approval obtained, and all resources have been allocated and scheduled, the project commences. As the project progresses, actual results start trickling in. These results could be activity progression on schedule, behind schedule, or ahead of schedule. When there is deviation from the estimated times, root cause analysis is performed, and appropriate corrections need to be carried out in the PERT chart.

Similarly, as the project unfolds with the progression of time, activities that were originally thought of as outside the Critical Path might suddenly threaten to upset the completion date of the total project. On the other hand, time estimates that were presumed to be quite intelligent guesstimates - based on expertise, experience, and what have you - seem to appear hollow. An ever-alert manager keeps themselves on their toes, learning every day of the project, and applying this knowledge about the men, material and the ground-realities involved to further fine-tune the future activities down the network diagram.

Conclusion

Over time, the original PERT chart notation has been modified so that activities are denoted as Nodes rather than arrows. The manager may decide to use any of these alternatives, which best suit their particular situation.

It is very easy for a project manager to get stuck in one single task or activity, or get bogged down with some particular event. There is always the risk of losing sight of the overall picture. To prevent this, one must continually consider the Critical Path and PERT chart.