Unit 6-2 Critical Path Method

The Critical Path Method (CPM) assumes that the duration of tasks are deterministic; i.e. only one estimate of task duration is needed. We will use the example below to show we determine the schedule of a project using the CPM method.

Suppose the table below represents the names, predecessor information and duration of tasks that make up a project or a sub-project. Before you continue, ask yourself this question: how are tasks durations typically arrived in project environments?


Predecessor Duration
a 5 days
b 4
c a 3
d a 4
e a 6
f b, c 4


h d, e 6
i f 6
j g, h 4

The first step is to draw a network diagram. Let’s use rectangles to represent the nodes of our network and we will use arrows to signify the completion of tasks, i.e. we are doing an AON diagram. Keep in mind that in preparing the diagram we move from left to right. The length of the arrows is irrelevant. The diagram should capture all the precedence relationships shown in the table. We will use two dummy tasks, one for the beginning of the project and another for the end. The initial diagram is shown here This is the basic Network ( or precedence) diagram also called the PERT diagram. initial-network-diagramx

Continue to the next learning unit to learn how to determine the schedule for this project.