Critical Path Method

BYDEEPAK ASNORA

GAURAV GARGADARSH SINGH

What is C.P.M.?The Critical Path Method or Critical Path Analysis, is amathematically based algorithm for scheduling a set of project activities

It is an important tool for effective project managementCommonly used with all forms of projects, including

construction, software development, research projects, product development, engineering, and plant maintenance, among others

Any project with interdependent activities can apply thismethod of scheduling

What is C.P.M.?The essential technique for using CPM is to construct

a model of the project that includes the following:

A list of all activities required to complete the project

(also known as Work Breakdown Structure).The time (duration) that each activity will take to

completion.The dependencies between the activities.

C.P.M. Contd…..CPM calculates

The longest path of planned activities to the end of the project

The earliest and latest that each activity can start and finish without making the project longer

Determines “critical” activities (on the longest path)Prioritize activities for the effective management and

to shorten the planned critical path of a project by: “Fast tracking" (performing more activities in

parallel) “Crashing the critical path" (shortening the

durations of critical path activities by adding resources)

How to use C.P.M.?1. Define the project and identify each activity2. Develop relationships among the activities.

(Decide which activities must precede and which must follow others.)

3. Draw the network connecting all of the activities

4. Assign time and/or cost estimates to each activity

5. Compute the longest time path through the network. This is called the critical path

6. Use the network to help plan, schedule, monitor, and control the project

7. Calculate the earliest start time, earlier finish time, latest start time & latest finish time.

8. Determine the total float for each activity on the basis of difference between the earliest time & latest time.

9. Calculate the total duration of project.10.Optimize the cost by shifting resources.

Network Diagram

1

2 3 4

8

5 6 7

IllustrationConsider the following schedule of activities & related information for the construction of a new plant:

Activity Expected Time Expected Cost

Rs. 1000Months Variance

1 – 2 4 1 5

2 – 3 2 1 3

3 – 6 3 1 4

2 – 4 6 2 9

1 – 5 2 1 2

5 – 6 5 1 12

4 – 6 9 5 20

5 – 7 7 8 7

7 – 8 10 16 14

6 - 8 1 1 4

Network Diagram of Problem

1

2

5

7

8

4

6

3

4 2

3

6

2

5

7

10

9

1

Calculations:Critical PathExpected cost of constructionExpected time required to build the plant

Solution:

From the above diagram, the critical path is1 – 2 – 4 – 6 – 8

The expected cost is:5 + 3 + 4 + 9 + 2 + 12 + 20 + 7 + 14 + 4 = Rs. 8,00,000

The expected time to build the plant is 4 + 6 + 9 + 1= 20 months

Limitations of CPMPrecise known time. ( Not true in real life)Changes affects the entire evaluationNot suitable for situation having indefinite

start & finishCPM is not a panacea for all ills it only

facilitates