Although project managers don't need to be experts in CPM scheduling or Gantt charts, the more they know about the preparing, updating and interpreting schedules, the better. Here some basics you need to know to be fully armed to read and critically analyze schedules:
1. CRITICAL PATH is the path which defines the duration of the project. It is the longest path in the schedule and ALSO the shortest amount of time the project can be completed in based on the assumptions underlying the schedule.
2. Activities on the critical path have a FLOAT of ZERO. By definition, if an activity has a duration of more than zero, it cannot be on the critical path.
3. Often, we can CRASH a schedule by adding resources to certain activities and/or re-sequencing work. The caveats are that there are limitations to crashing and there are diminishing returns.
4. Complex projects can have more than one critical path.
5. In a dynamic project, the critical path can change and this needs to be monitored as it has contractual implications.
6. A schedule should have sufficient detail and align with the cost reporting system. A schedule with insufficient detail can present project management and reporting problems. And a schedule with too much detail creates a burdensome tool.
7. A schedule is a management tool and if you use it only as a reporting tool, you defeat the purpose of the schedule.
8. The PM must ensure that the logic driving the scheduled activities is clear and correct.
9. The monthly schedule update MUST be presented with a narrative explaining how the schedule was advanced, what risks were manifested, potential new risks to the schedule and any changes to the critical path.
Project managers must ask questions when evaluating schedules. Are durations accurate? Are the logical ties consistent? Is the schedule consistent with the project manager's experience on similar projects?
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Ravi, actually tasks on the critical path by definition will have durations more than 0, but as you stated no float time. Also, there should be ONLY one critical path per project or there would be conflicts by definition.