We looked at few concepts in this post –
- Critical path
- Critical path in a network schedule diagram is the network path with longest total duration
- Critical path sure is the longest network path, but this indicates Shortest Duration of the project – which means any activity slipping on this path will cause a delay in project completion
- It is calculated by simply adding up duration of all activities on each network path and finding the one with largest number
- Float (also known as Slack) of an activity is the duration that it can slip without delaying the next activity or the project end date
- Float for every activity on critical path is zero
- Float for every activity on a network path is the difference between its total duration and that of critical path (excluding the activities that have float calculated already)
- Float is calculated for network paths in the descending order of their total duration, starting with critical path
- Calculating Early and Late Starts and Finishes
- Early start and finish are calculated by forward pass through the network path, and Late start and finish are calculated by backward pass
- Both are calculated first for the critical path
- Both are calculated for remaining network paths in the descending order of their total duration
- During calculation if you come across any activity with duration already calculated, do not overwrite
Here’s a video explaining nicely the concept of Critical path, Float and network diagram using Forward and Backward pass.
Note that he uses the convention of starting on day 0 and so NOT adding a day to start next activity. On the contrary, I use the convention of starting an activity on day 1 and adding 1 to start next activity on subsequent day, as this feels natural for our understanding.
You can use any convention you feel comfortable with, just know that the question on exam might present scenario using any of these conventions – so knowing both will help you answer them easily.
These calculations are quite simple once you get a hang of it. Good luck!