Critical Path Method, or CPM, is a project modeling technique that helps project managers plan, schedule, and execute their projects effectively. It pinpoints the crucial tasks — the ones that, if delayed, would push back the project's entire timeline.

1. PERT/CPM
Durga Prasad Pahari
DCMFH, MMC, IOM

2. CPM: Critical Path Method (Industrial Origin)
PERT: Program Evaluation Review Technique
(Military Origin)
– Tools of Project Management
– Helps in Planning, Monitoring, Controlling and
Decision making

3. Introduction - CPM
• Complex projects require a series of activities
– Some must be performed sequentially
– Others can be performed in parallel
• This collection of series and parallel tasks can
be modeled as a network.
• In 1957, the Critical Path Method (CPM) was
developed as a network model for project
management. (Chemical Plant Establishment)

4. CPM Contd...
• The Critical Path Method (CPM) is one of the
techniques for doing project planning.
• CPM is a method that uses a fixed time
estimate for each activity.
• CPM does not consider the time variations
that can have a great impact on the
completion time of a complex project.

5. • CPM is for projects that are made up of a number of
individual ‘activities’.
• CPM can help us figure out
- how long our complex project will take to complete
- which activities are "critical," meaning that they have
to be done on time or else the whole project will take
longer
CPM Contd...

6. CPM Contd...
• CPM analysis starts after we figured out all the
individual activities in our project.
• Tasks which fall on the critical path should
receive special attention by both the project
manager and the personnel assigned to them.

7. CPM Contd..
• Notice that there are three paths through the network:
• Path A-C B-D A-D
• Length 6 7 8

8. CPM Contd..
• The critical activities are those which lie on a
longest path through the network - here A and
D are critical.
• A longest path through a network is called a
critical path.

9. PERT
• PERT is a method to analyze the tasks involved in
completing a given project, especially the time needed to
complete each task.
• Developed by Booz-Allen Hamilton (US Navy special
project office) in 1958 as a method to plan and control
the Polaris Missile program.
• Developed to simplify the planning and scheduling of
large & complex project
• Event oriented techniques applicable to projects where
time rather than cost is a major factor.
• The Program Evaluation and Review Technique (PERT) is a
network model that allows for randomness in activity
completion times.

10. PERT Contd…
• The basic tools used in PERT approach is the network
or flow plan.
• The network is composed of a series of related
events and activities.
– Events are required sequential accomplishment points in
the program or project
– Activities are the time consuming elements of the
program and actually connects the various events
• Many activities and events are involved in a program
or a project.

11. • PERT can be very useful in planning and
controlling
• Three basic characteristics of a program or
project that is amendable to the PERT
approach.
– Activities be such that time estimate can be
made
– There must be starting and ending points
– There must be parallel activities – key to PERT
usefulness
PERT Contd…

12. PERT Contd..
• The most recognizable feature of PERT is the
"PERT Networks", a chart of interconnecting
timelines.
• PERT is intended for very large-scale, one-
time, complex, non-routine projects.

13. Importance and Use of PERT
• A PERT chart is a tool that facilitates decision making
• Two consecutive events in a PERT chart are linked by activities,
which are conventionally represented as arrows in the diagram
above.
• The events are presented in a logical sequence and no activity
can commence until its immediately preceding event is
completed.
• The planner decides which milestones should be PERT events
and also decides their “proper” sequence.
• A PERT chart may have multiple pages with many sub-tasks.

14. Decision to develop
Open heart surgery
Unit.
Planning complete
Equipment
ordered
Equipment
received
Equipment ins
talled
Equipment and
team tested
and ready
Operating room
gutted
Renovation
complete
Team recruited Team hired Team trained
5-7-9
1-2-3
10-12-14
3-4-5
1-2-3
2-3-4
2-3-4
3-4-5
2-3-4
2-3-4 4-5-6
1-2-3
Critical
Path
1-2-3 = Indicates, in order of listing estimates of most optimistic, most likely,
and most pessimistic completion times
Source: Longest , Beaufort B,
Example: PERT network for developing a open heart unit

15. PERT Contd..
• To make the network understandable and usable, the time
between the various events (activity time) must be computed.
• No accurate method to estimate time, however, optimistic
time (OT), most likely time (MT) and pessimistic time (PT) can
be estimated
• Calculate activity time by dividing OT+4MT+PT divided by 6
• Critical path: the path that takes the longest period of time to
complete

16. Steps in the PERT Planning Process
• Identify the specific activities and milestones.
• Determine the proper sequence of the activities.
• Construct a network diagram.
• Estimate the time required for each activity.
• Determine the critical path.
• Update the PERT chart as the project progresses.

17. Benefits of PERT
PERT is useful because it provides following information
• Expected project completion time
• Probability of completion before a specified date
• The critical path activities that directly impact the
completion time
• The activities that have slack time and that can lend
resources to critical path activities
• Activity start and end dates

18. Limitations
• The activity time estimates are somewhat subjective
and depend on judgment.
• PERT assumes that the probability distribution of the
project completion time is the same as the that of
the critical path. PERT consistently underestimates
the expected project completion time.

19. Thank You!!!