Project Critical Path and How its done in Microsoft Project

The critical path of a project is important: the time to complete all the tasks on the critical path is the time it takes to complete the project.

Project managers must focus on tasks on the critical path without loosing site of the other project tasks.

Identifying and monitoring the critical path of large projects would be time consuming and error prone without the use of project management tools such as Microsoft Project.

To illustrate the basic ideas associated with the critical path of a project we shall use a simple project detailed in table 1.

Note- we suggest you create a project plan of the sample project in MSP and use it see how things work

We also suggest you draw the network diagram.

The project plan has been created in MicroSoft Project 2010 (MSP2010) - to carry out the exercises below you will need a copy of MSP2010.

Table 1 Sample Project Task Details
Task ID Duration days Predecessors Comments
T1 10

 

Task identifiers have been given simple names, T1, T2 etc.
T2 5 1 In a real project meaningful task names would be used, such as Plan Software, Debug Software, Documentation etc.
T3 4 2 Task durations are all in days.
T4 12 3 T1 does not have a predecessor, it is the first task
T5 15 4,8  
T6 20 1 The network diagram can be drawn using the task predecessors
T7 12 2,6  
T8 15 7  
T9 2 1  
T10 5 7,9  
T11 4 10  
Finish 0 5,11 The finish task has zero duration, it is a milestone

 

 

Projects are undertaken by most organisations.

When a company decides to develop a new product, for example, it is a very important project, now matter how big or small the company is.

Project must be managed effectively.

Projects are broken down into tasks, which are usually broken down into sub tasks, etc.

A critical aspect of all projects is completion time: if a project finishes on time it is more likely to be in budget.

Some project tasks may be carried out at the same time as other tasks.

The critical path of a project is the sequence of tasks that take the longest to complete.

In Table 1, Task T1 is the first task on the project.

Task T1 is called the predecessor of T2.

All the tasks on the project have a predecessor, except the first.

Note that T5 has two predecessors, T4 and T8.

When all the predecessors are known it is possible to plan the project.

The project manager, usually working with other members of the project team, decides the task predecessors.

Figure 1 has been drawn using the project task predecessors.

MSP uses task predecessors to draw project network diagrams and Gantt charts.

We have used a very simple project to illustrate the critical path.

Figure 1 The Sample Project Network Diagram showing the Critical Path

Figure 1 The Sample Project Network Diagram showing the Critical Path

 

The critical path is the longest path through the network diagram.

The duration of the critical path is the time it takes to complete the project.

The critical path and its duration is-

T1+T6+T7+T8+T5

10+20+12+15+15=72 days

The time to complete other paths is less than 72 days.

Just try one or two paths off the critical path to convince yourself.

Even in relatively small projects, involving 60 tasks say, computing the critical path manually can be time consuming and error prone.

In large projects calculating the critical path by hand can be a major undertaking.

Note- during project implementation the critical path may change: if a task not on the critical path takes much longer than expected a new critical path may be created.

MicroSoft Project (MSP) monitors the critical path and allows the project manager to always ensures it is up to date.

The sample project listed in Table 1 is shown in Gantt Chart format in Figure 2, in MSP.

Figure 2 The Sample Project Gantt Chart View in MSP

Figure 2 The Sample Project Gantt Chart View in MSP

To select the Gantt chart view-

Select Task/Gantt Chart/Gantt Chart

The name of the view, in this case Gantt Chart, is shown on the far left of the screen (vertical grey bar).

Note MSP has drawn the Gantt chart- it does that as soon as the task predecessors are entered.

For tasks with multiple predecessors, predecessors are separated with commas.

Durations have been entered in days.

Durations are actually working days, for example they do not include Saturdays and Sundays.

 

Figure 3 The Critical Path in the Gantt Chart View

Figure 3 The Critical Path in the Gantt Chart View

To show the critical path in the Gantt Chart View-

Select Format/Critical Tasks

The critical path is shown in red, by default.

We have used a milestone to show when the project finishes.

The project starts on the 19 April, 2013 and finishes on the 29th July, 2013.

This is longer than 72 days, because of weekends, which are none working days.

This is made clear in the project time line.

MSP generates the project network diagram, which is shown in figure 4.

Figure 4 The Sample Project Network Diagram in MSP

Figure 4 The Sample Project Network Diagram in MSP

To display the project network diagram-

Select Task/Gantt Chart/Network Diagram

The network diagram matches that shown in figure 1.

The critical path is shown in red.

To see the details of a task hover your mouse over it.

The network diagram is very useful for identifying task that are not linked to others, that is that have no predecessors defined.

If some tasks have no predecessors defined calculation of the critical path can be ambiguous.

The milestone used for the project finish allows us to ensure that no tasks are left unlinked.

 

Figure 5 The Tracking Gantt View of the Sample Project in MSP

Figure 5 The Tracking Gantt View of the Sample Project in MSP

There are numerous views we can use in MSP.

Figure 5 shows the tracking Gantt Chart.

To see this view-

Select Task/Gantt Chart/More Views/Tracking Gantt Chart

This is used to track the progress of a project when it is being implemented.

Note that each task has 0% associated with it: this means that none of the tasks have had any work done on them yet.

During project implementation the project manager should ensure that the progress of tasks are entered into the project plan.

If task T1, for example, had been set to 60% complete, this would be shown on the Tracking Gantt Chart.

The critical path is shown in red.

Figure 6 The Sample Project Detail Gantt Chart

Figure 6 The Sample Project Detail Gantt Chart

To view the Detail Gantt Chart-

Select Task/Gantt Chart/Detail Gantt

The black lines show the slack associated with a task, or groups of tasks.

The slack associated with task T4 is 26 days.

Task T4 could be started later than 16/05/13 without delaying the project.

The critical path would not be affected.

 

Figure 7 The Gantt Chart using an Expanded Time Scale

Figure 7 The Gantt Chart using an Expanded Time Scale

The time scale of any Gantt chart can be controlled.

Right click anywhere on the time scale, e.g. 29th April.

In the popup click time scale.

In the new popup select middle tier, set units to weeks and count to 1.

Then select bottom tier, set unit to days and count to 1.

The result should be like that shown in figure 7.

Note, Task T1 has a duration of 10 working days, but it takes 14 days to complete because it spans 2 weekends, which have been set to non-working time.

The project has used the MSP standard calendar, which defaults to Saturday and Sunday as non- working time.

Note, there are numerous views and facilities in MSP, the best way to become familiar with them is by practice.

We suggest you use small example projects to develop your skills.