RE: CPM

Hi Rebekah

Thanks for your question. The Critical Path Method is a way of finding out the earliest date your project can be delivered and also identifies those tasks that have no slack or float around them and also determine the end date of the project.

After creating a network diagram for your project you would then work out:

Earliest Start ES
Earliest Finish EF
Latest Start LS
Latest Finish LF

for each of your tasks.

Step 1 Forward Pass:
Work out the ES for each of your tasks, starting left to right.
A task's ES is the sum of its predecessor durations.

The EF can be calculated as ES + activity duration

Step 2 Backward Pass:
The LF is the latest date the activity can finish without affecting the end date of the project. This process starts at the end of the project and works back toward the start.

The LS is the LF - activity duration

Step 3
You can now calculate float within your project.
Float is LF - EF

The advantage of applications such as Microsoft Project is that they calculate all of this automatically for you and can highlight the critical path directly on the Gantt Chart.

I hope this helps. do let us know if you have any other questions.

Kind regards,

Andrew