Part of project planning and critical path calculation by the PERT method requires the development of a network diagram that clarifies the relationships between activities of a project. In this post you will find out how to create a PERT Chart step by step with practical examples.
It is important to point out that in this publication we will only focus on the elaboration of the PERT network diagram; the calculations for the determination of the critical path will be dealt with in a future post.
We remind you that with our critical path method calculator you will be able to create your PERT chart easily and automatically.
What is a PERT chart?
The PERT chart is a graphical representation of the project network, which shows the sequence of activities of a project and the dependency relationships between them, in order to facilitate and help managers to monitor and control projects.
An activity “B” depends on another “A”, when activity “B” cannot start until activity “A” is finished. To give an example, we have the following project activities:
- Activity A: Design plans for the construction of a house.
- Activity B: Print the plans to give to the contractor.
If the plans aren't designed first (A), they cannot be printed (B); therefore, activity “B” is considered to be dependent on activity “A“. You can also say that activity “A” precedes activity “B“.
The relationship between the activities described is known as “Finish to start (FS)“. There are 3 types of relationships for other types of more complex projects; however, for our network diagram we will use FS.
What Is the Difference Between PERT Chart and CPM Chart?
It is also important to note that, although the PERT and CPM methods have some differences in their application, both techniques require the development of the network diagram. That is why, in other literature, this graph is known as CPM network diagram or CPM chart. Even so, at present the differences between the two techniques are minimal and, on the contrary, they complement each other to form a broader theory.
(AOA) and (AON) networks
Depending on the way the activities are represented, our PERT network can be drawn one of two ways:
- Activities on nodes (AON): The nodes in the graph represent the activities of the project, and the arrows show the relationship with the immediate predecessor.
- Activities on arrows (AOA): The arrow indicate the activity and their starting and terminating points are represented by the nodes.
Our PERT chart can be represented using both ways; however, here we'll explain the AON network diagram.
Below are the AON graphical representations for certain relationships that occur in project activities:
1. A comes before B, which comes before C.
2. A and B must both be completed before C can start.
3. B and C cannot begin until A is completed.
4. C and D cannot begin until both A and B are completed.
5. C cannot begin until both A and B are completed; D cannot begin until B is completed.
6. B and C cannot begin until A is completed. D cannot begin until both B and C are completed.
At this point you should already have a clearer idea of how to draw and link your activities according to the relationships they have.
How to create a PERT Chart step by step
Here is a step-by-step procedure to create a PERT chart with activities in nodes:
- Step 1: List all the project's activities: In the first place, identify all activities and tasks necessary to complete the project.
- Step 2: Determine which dependencies exist: It is important to identify the interrelatedness of the activities in order to map out the routes to take on the project.
- Step 3: Drawing the nodes: The activities identified in point one will be drawn as nodes in the diagram.
- Step 4: Mapping dependencies: Once the activities have been represented, the nodes should be joined with arrows according to the dependency relationships. Crossings between the lines should be avoided as much as possible.
To better understand how to create a PERT diagrams, we will examine some examples:
Examples of PERT Chart (AON Network):
Draw the activity-on-node (AON) project network associated with the following activities for Dave Carhart's consulting company project.
To start our network diagram, we place a fictitious node that establishes the beginning of our project and from where the first activities, which have no precedents, will come from (Activity A):
Activities B and C start after activity A is completed:
Activities D and E depend on activity B:
Activity F has activity C as its immediate precedent and activity G depends on activity D:
Activity H depends on two activities: E and F; therefore it must be connected to both nodes:
Activities G and H, which are the final activities, are joined to a dummy node representing the end of the project:
The above graph represents our PERT network diagram of the example project.
The director of continuing education at Bluebird University just approved the planning for a sales training seminar. Her administrative assistant identified the various activities that must be done and their relationships to each other, as shown in Table 1.
Table 1: Activities for the sales training seminar
|A||Design brochure and course announcement||—|
|B||Identify prospective teachers||—|
|C||Prepare detailed outline of course||—|
|D||Send brochure and student applications||A|
|E||Send teacher applications||B|
|F||Select teacher for course||C, E|
|H||Select text for course||F|
|I||Order and receive texts||G, H|
|J||Prepare room for class||G|
Determine the PERT network chart to conduct the seminar.
We start our graph with the start node connected to the activities that have no precedents (A, B and C):
Activity D and E depend on activities A and B respectively:
We connect activity F to its preceding activities (C and E):
Activity G and H have as precedents activities D and F respectively:
Activity I depend on activities G and H, and activity J depends only on activity G:
Finally, we connect the last nodes to the finish node, and we will have our complete diagram:
The PERT chart gives us a simple view of the activities of a project and their precedence relationships; it also represents the starting point for the determination of the critical path of the project; therefore it is very important for project managers to elaborate it correctly.
In our next post we will discuss the calculation of the critical path.