1. Critical Path Method
By Matthew Gordon
IST 402 – Professor Kochanov

2. History/ Background Critical Path Method (CPM)
Du-Pont wanted a better method to build and maintain its chemical plants.
The availability of computers such as UNIVAC 1 assisted in development.
CPM can be used for varying types of projects ranging from simple to extremely complex.
Origins from 1956 to 1958.
US government wanted to shorten Polaris missile construction time, so they used "Program Evaluation and Review Technique" (PERT).
Reduced there development time 45% (2 years in this case).
Du-Pont wanted a better method to build and maintain its chemical plants.
The availability of computers such as UNIVAC 1 assisted in development.
Around the same time CPM was being developed by DU-Pont.
They used CMP or at that time the Kelly-Walker method to plan construction of a $10 million dollar chemical plant.
The resulting network diagram had more than 800 activities.
It was so successful that DU-Pont use it the next year for a $20 million dollar project.
CPM can be used for varying types of projects ranging from simple to extremely complex.

3. What is the Critical Path Method
Provides a way to identify how quickly a project can be completed.
Shows which activities could be time bottlenecks.
Tends to use Network Diagrams for visual representation of durations.
Inputs for each Activity:
Expected duration.
Immediately proceeding activity.
Provides a way to identify how quickly a project can be completed.
If estimated durations of activities are correct
Helps identify where a project will require the most amount of time and where it could get hung up if a task is not completed.

4. How CPM Can Be Used
The most simple form would be a table listing the inputs for the activities:
Task ID
Task Description
Duration (Seconds)
Prerequisites
Turn on water 3
None 1
Apply Soap 5 2
Wash Hands 60
Dry Hands 12
But you could also make it into a simple Network Diagram:

5. More Ways to Use CPM
GANTT Chart:

6. Additional Schedules Early Start: Late Start: Slack:
Earliest a task can start assuming its predecessors are complete.
For every activity that has scheduled predecessors, schedule it to start ASAP.
Late Start:
The latest a task can start and allow the project to stay on track.
Slack:
Difference between Late and Early Start Schedules.
Tasks with zero slack, must be completed on time or they will delay the project.

7. Critical Paths A project can have more than one critical path.
Shortest amount of time a project can be completed in.
Can be depicted via:
GANTT charts
Network Diagrams
Arrow on Node diagram (AON)
Arrow on Arrow diagram (AOA)
Project can have more that one critical path since two paths in the project could be equal in duration.

8. Buffers Project Buffers Feeding Buffers
Used to pad a project to ensure it finishes on time.
Feeding Buffers
Used where a non-critical activity affects one on the critical path.
Also allows for early start of critical path item.

9. Buffers Resource Buffers Strategic Resource Buffers
Ensures the availability of resources including people; i.e. if a employee is able to work on a project earlier than expected.
Strategic Resource Buffers
Designed to ensure that key resources are available for critical activates.

10. Resource Leveling
Designed to allow for the most efficient use or a resource without over scheduling the resource at the same time.
Methods:
Schedule tasks that require a certain individual or equipment close together if at all possible.
Don’t bring equipment or staff on site until needed.

11. Criticisms
It’s a mathematical model that assumes everything will go as planned.
Assumes unlimited resources and their constant availability.
Assumes that tasks have a clear beginning and end, and does not address the possibility of variations in task duration.
Assumes project requirements will not change during project.

12. Questions ? Effect on ERP projects?
Since IT project tend to go off schedule this method might not be adequate to determine the total duration of the project.

13. Works Cited
HPC. “History of Critical Path Method.” < vices/planning_academy/04-cpm-history.asp> 3/13/2005.
Olson, David. “Managerial Issues of Enterprise Resource Planning Systems.” McGraw- Hill/Irwin. New York, New York pp
Witcombe, Mike. “Critical Analysis.” < inc.com/projex/PERT/aon.htm> 3/13/2005.