Answer:
Float is one of the very basic concepts essential for building network diagrams and in turn a project schedule. Further, there are different types of floats such as Free float, Total float, Project float, Interfering Float, Independent Float. As a Project Manager, you should have a clear understanding of these concepts in order to create efficient project schedules.
The term “Float” implies “Fluid”, which in turn implies “Flexibility“. In Project Scheduling, Float refers to the amount of scheduling flexibility. Float is also popularly called “Slack“
Difference between Total Float, Free Float, Independent Float
Activity float analysis provides the information on the margin on allowance available for the commencement and completion of various activities. Activities with zero slack value represent activities on the critical path. Three types of activities floats are identified:
- Total float
- Free float
- Independent float
Total Float :Total float usually referred to as simply float or slack, is the amount of time an activity can be delayed beyond its earliest possible starting time without delaying the project completion, if other activities take their estimated duration.
Total float for activity (i-j) = LOT(i) – EOT(i) – d(i-j)
Free Float : Free float is the amount of time on the basis of which an activity can be delayed without delaying the early start of a successor activity. To find free float, we subtract the early finish of an activity from the early start times of its succeeding activities.
Free float for activity (i-j) = EOT(i) – EOT(i) – d(i-j)
Independent Float :This indicates the time span by which the activity (i-j) can be expanded or shifted if, for the event (i) the LOT and for the event (j) the EOT shall be maintained. A shifting of activity in this area has no influence on the further progress of the project. Independent float is taken as zero is negative.
Independent float for activity (i-j) = EOT(i) – LOT(i) – d(i-j)
The floats of various activities of our illustrative project are shown in Table 1
| Activity | Duration | EST | EFT | LST | LFT | Total | Free | Independent |
| 1-2 | 13 | 0 | 13 | 0 | 13 | 0 | 0 | 0 |
| 1-3 | 12 | 0 | 12 | 6 | 18 | 6 | 0 | 0 |
| 2-4 | 2 | 13 | 15 | 24 | 26 | 11 | 5 | 5 |
| 3-4 | 8 | 12 | 20 | 18 | 26 | 6 | 0 | -6 i.e. 0 |
| 2-5 | 15 | 13 | 28 | 13 | 28 | 0 | 0 | 0 |
| 4-5 | 2 | 20 | 22 | 26 | 28 | 6 | 6 | 0 |
