The Metra Potential Method (MPM)

To understand the mechanics of the PERT, let’s take a simplified example, namely a project that requires the completion of 5 tasks.

Some tasks require the completion of other tasks to be performed.

When we integrate this information into a PERT model, we obtain the graph below:

At the start date, we can launch two tasks simultaneously (A and B). Task C requires the completion of task A. And task D requires the completion of tasks A and B.

Task A takes 2 time units (days in our example) to complete, whereas task B takes 4 days. Thus, task D cannot start before 4 days.

Once this logic is integrated, we can determine a critical path (marked in red on the graph) which represents the longest sequence of tasks between the start and the end of the project. It corresponds to the uncompressible time for project execution.

Although this example is simplified, in reality, PERT graphs can contain hundreds of different tasks and span several months, or even years.

In general, it is always true that a graph has a start and end date. Between these two dates, each task is represented by a vertex.

For each task, we know its duration, its start date (at the earliest and the latest).

The graph is read from left to right and the succession constraints between the tasks are symbolized by arrows (called arcs) which represent the precedence relationships of the tasks.

From this graph, we can determine the critical path of the project which corresponds to the longest sequence of tasks between the start and the end of the project.

The PERT method allows us to have a visual representation of the project organization and to quickly know its uncompressible duration. 

→ Learn more about the different scheduling methods