Critical Path Method (CPM)

Critical Path Method (CPM) is a method used in project planning, generally for project scheduling for the on-time completion of the project. It actually helps in the determination of the earliest time by which the whole project can be completed. There are two main concepts in this method namely critical task and critical path.

Critical task is the task/activity which can’t be delayed otherwise the completion of the whole project will be delayed. It must be completed on-time before starting the other dependent tasks.

Critical path is a sequence of critical tasks/activities and is the largest path in the project network. It gives us the minimum time which is required to complete the whole project. The activities in the critical path are known as critical activities and if these activities are delayed then the completion of the whole project is also delayed.

Major steps of the Critical Path Method:

1.Identifying the activities

2.Construct the project network

3.Perform time estimation using forward and backward pass

4.Identify the critical path

The table given below contains the activity label, its respective duration (in weeks) and its precedents. We will use critical path method to find the the critical path and activities of this project.

ACTIVITY	PRECEDENTS	DURATION
A	–	6
B	–	4
C	A	3
D	B	4
E	B	3
F	–	10
G	E, F	3
H	C, D	2

Rules for designing the Activity-on-Node network diagram:

· A project network should have only one start node

· A project network should have only one end node

· A node has a duration

· Links normally have no duration

· “Precedents” are the immediate preceding activities

· Time moves from left to right in the project network

· A network should not contain loops

· A network should not contain dangles

Node Representation :

Forward path :

Backward path:

Critical path: