Scribd
Upload
236 views3 pages

Critical Path Method: M.R. Walker & J.E. Kelley of Ramination R& Developed CPM For The

The document compares and contrasts the Critical Path Method (CPM) and Program Evaluation and Review Technique (PERT). CPM was developed for construction projects and uses a deterministic approach with a single time estimate for activities, while PERT was developed for research and development projects and uses a probabilistic approach with three time estimates for events. Both techniques are used to plan and control projects by identifying the critical path of activities/events. Float types such as total float, free float, and interfering float are defined and used to classify activities as critical, subcritical, or super critical.

Uploaded by

ramesh sitaula
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
236 views3 pages

Critical Path Method: M.R. Walker & J.E. Kelley of Ramination R& Developed CPM For The

The document compares and contrasts the Critical Path Method (CPM) and Program Evaluation and Review Technique (PERT). CPM was developed for construction projects and uses a deterministic approach with a single time estimate for activities, while PERT was developed for research and development projects and uses a probabilistic approach with three time estimates for events. Both techniques are used to plan and control projects by identifying the critical path of activities/events. Float types such as total float, free float, and interfering float are defined and used to classify activities as critical, subcritical, or super critical.

Uploaded by

ramesh sitaula
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 3

CPM & PERT 761

Critical Path
Method 4
M.R. Walker & J.E. Kelley of Ramination R& developed CPM for the
construction of chemical plants in United States.
Comparison between PERT & CPM
PERT CPM

1. Probabilistic approach 1. Deterministic approach

2. Event oriented 2. Activity oriented.

3. Three time estimate 3. Single time estimate


4. Use in construction
4. Use in R&D project
having prior exprience
5.  -distribution 5. Normal distribution
6. Cost is proportional to 6. Cost model is developed
time

7. Concept of slack 7. Concept of float

8. Critical path by joining 8. Critical path by joining


critical events critical activities.
9. Non-repetitive nature 9. Repetitive nature
10. A technique of planning 10. A method to control cost
& control of time & time

Start & finish times of activity

Earliest start Latest start Earliest finish Latest finish


time (EST) time (LST) time (EFT) time (LFT)
(EST)ij = TEi
j
(LST)ij = TL– t ij (EFT)ij = TEi + tij (LFT) = TL
j

Float: It indicates the time by which, starting or finishing of an activity


can be delayed without affecting the project completion time.
762 Civil Booster (Civil Ki Goli Publication 9255624029)

Activity Name (EST, EFT)


 (i) t ij  x days (LST, LFT) ( j)

 Float is associated with An activity.


1. Total Float: It is the difference between maximum time available &
actual time required for the completion of the activity.
2. Free Float: It is the amount of time by which an activity can be delayed
without affecting the EST of the succeeding activity
3. Independent Float: It is the excess of minimum available time over
the required activity duration.
4. Interfering Float: It is the difference of total float & free float of an
activity. It is also equal to the slack of head event of an activity.

For activity ‘X’ of 5 day duration.


Total float = 65 –10 – 5 = 50
Free float = 55 – 10 – 5 = 40
Independent float = 55 – 30 – 5 = 20
CPM & PERT 763

Interferring float = 65 – 55 = 10
or TF – FF = 50 – 40 = 10

float Type

Total float > 0 Total float < 0


Total float = 0
Subcritical Super critical
activity Critical
activity activities
Demands normal Needs extra
attention but No freedom
of delay deployment
some freedom of of resources
delay is allowed is allowed

Special Point: For critical path, all four floats are generally zero as critical
path passes through those events where slack is zero & this is only a
necessary condition but it is not sufficient condition.

You might also like