Precedence Diagramming Method Example

Precedence Diagramming Method (PDM) is a visual representation technique which is used to prepare the project network diagram and determine the critical path. Unlike the arrow diagramming method , activities are presented as boxes in PDM. One of the main advantages of the Precedence Diagramming Method (PDM) is that it demonstrates the activity relationships. This article reviews a Precedence Diagramming Method Example and analyzes the basics of this method.

It is critical for a project manager to realize the activity relationships because it is important while preparing the network diagram and then creating the project schedule.

For better understanding, let’s analyze the example below and follow the steps.

Precedence Diagramming Method Calculation Steps

 

In this example A,B,C,D,F,G,H,I are the activities. Numbers above the boxes are the durations. Activity B is a predecessor activity that logically comes before a dependent activity F in this network system. Activity F is a successor activity that logically comes after the Activity B. There is a F-S Relationship between activity B and F.

Step 1 : PDM Forward Pass Calculation

In this Precedence Diagramming Method Example, we will perform forward and backward pass calculations. Forward Pass Calculations specify the minimum dates at which each activity can be performed and, ultimately, the minimum duration of a project.

Step 2 : PDM Backward Pass Calculation

Backward Pass Calculations determine the latest dates by which each activity can be performed without increasing the projects minimum duration.

Step 3 : PDM Float Calculation for Each Activity / Precedence Diagramming Method Example

Total float is the amount of time that an activity can be delayed without delaying the project completion date. Total float is 0 on the critical path.

Total Float: LS – ES = 17-7 = 10
Total Float: LF – EF = 27-17 = 10

Total float can be calculated by subtracting the Early Start date of an activity from its Late Start date or Early Finish date from its Late Finish date.

Step 4 : PDM Identifying the critical path / Precedence Diagramming Method Example

When we analyze the network diagram we will see that there are some paths and every path have duration.
The critical path is the longest path in the network diagram and the total float of the critical path is zero.

Summary

In this article, we review a Precedence Diagramming Method Example. In this simple example, we show how to make forward, backward, total float and critical path calculation. The Precedence Diagramming Method (PDM) enables us to make these calculations correctly. By the help of a tool like Primavera P6 , it is very easy to make these calculations.

Tags: CPM Critical Path PDM Method Precedence Diagramming Method Example Total Float