Critical Path Method for Project Scheduling

When managing a project, we may use critical path method to identify the activities that govern the entire progress.

To do so, we first define all the activities required and estimate their duration.

Then, we also need to know their dependencies with each other.

Afterwards, we can proceed with the construction of precedence diagram. It is common to use activity-on-node (AON) notation here.

When the diagram is ready, we carry out forward and backward pass to determine the early start, early finish, late start and late finish for all activities. Finally, we calculate the total float for each of them.

An activity is on critical path if its total float is zero.

Here we prepared an info sheet to outline the procedure to conduct critical path method.

In this worked example, we are required to plan for a project that consists of 10 tasks. The task duration and their dependencies among each other are determined beforehand. We aim to determine the critical path for this project by using critical path method (CPM).

First, we construct the frame of precedence diagram based on the dependencies.

Then, we use forward pass to determine the early start (ES) and early finish (EF) for all tasks. At the end of forward pass, we should be able to know the completion date of our project.

After that, we use backward pass and find the late start (LS) and late finish (LF) for all tasks.

Next, we can calculate the total float (TF) for all tasks. This value tells us to which extent we can be delay a task without hindering the progress of the entire project.

Finally, we can determine the critical path by highlighting the task with TF equals to zero.