Page 153 - DCAP601_SIMULATION_AND_MODELING

Unit 9: Simulation of a PERT Network (I)

3. The Latest Finish is the value in the diamond at the head of each activity Notes

4. The Latest Start is = Latest Finish - Duration
There are two significant types of Float or Slack. These are Total Float and Free Float.
TOTAL FLOAT is the spare time available when all earlier activities occur at the earliest possible
times and all succeeding activities occur at the latest possible times.
Total Float = Latest Start - Earliest Start
Activities with zero Total float are on the Critical Path

FREE FLOAT is the spare time available when all previous activities occur at the earliest possible
times and all succeeding activities occur at the earliest possible times.
When an activity has zero Total float, Free float will also be zero.

There are a variety of other types of float (Independent, Early Free, Early Interfering, Late Free,
Late Interfering), and float can also be negative. We shall not go into these situations at present
for the sake of simplicity and be concerned only with Total Float for the time being.

Having calculated the various parameters of each activity, we are now ready to go into the
scheduling phase, using a type of bar chart known as the Gantt Chart.
There are various extra types of float (Independent, Early Free, Early Interfering, Late Free, Late
Interfering), and float can also be negative. We shall not go into these situations at present for
the sake of plainness and be concerned only with Total Float for the time being. Having computed
the various parameters of each activity, we are now ready to go into the scheduling phase, using
a type of bar chart known as the Gantt Chart.

Did u know? What is the difference between Total Float and Free Float?
Total Float is the spare time available when all preceding activities occur at the earliest
possible times and all succeeding activities occur at the latest possible times.

Free Float is the spare time available when all preceding activities occur at the earliest
possible times and all succeeding activities occur at the earliest possible times.

Scheduling of Activities using a Gantt Chart

Once the activities are laid out along a Gantt Chart (Please see chart below), the concepts of
Earliest Start & Finish, Latest Start & Finish and Float will become very obvious.

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