A. Explain how the critical path is used for project tracking purposes.
Using Critical Path Method will help identify and coordinate various tasks associated with the completion of a project. Critical Path Method (CPM) was developed in the 1950s as a way of organizing and tracking the numerous activities associated with the Polaris missile defense program. It would be easy to track the total time to complete the project, scheduled start and finish dates for each task pertaining to the project’s completion, tasks that are “critical“ to the project and must be completed exactly as scheduled with out any delay. ‘Slack’ is the time available in non-critical tasks and the amount of time they can be delayed before they affect the project finishing date. If any of the tasks on the critical path are delayed then the entire project will be delayed. To begin determining the critical path, we must first determine the earliest start time and a latest finish time for all tasks. ES= earliest start time, EF= earliest finish time, the earliest finish time for a task is; EF= ES+t Assuming the network we begin from the start. Task 1, can begin as soon as possible, so we set its t to 0 (t= 0). It has time of 1 week so its earliest finish time will be: EF=0+1 = 1. Since the task cannot be started until all other preceding tasks have finished the earliest start time for a task is equal to the largest of all the earliest finish times for all its immediate predecessors. We make a forward pass through the whole network determining all the earliest start and finish times for all tasks. The earliest finish time for the last task will be how long the entire project will take to complete. We now make a backward pass through the network to determine the critical path. Since we assume that the project will take 20 weeks to complete. This will be our latest finish time. LF= latest finish time, LS= latest start time. The latest start time for the last task will be: LS=LF-t
Moving backwards, the latest finish time for a task is the smallest of the latest start times for all tasks that immediately follow that task. The latest finish time is the earliest start time for the immediately following tasks. Once we have completed the forward and backward passes through the network, we can determine how much “slack” in each task that is the length of time the task can be delayed without it affecting the project completion date. Slack is determined as follows: Slack=LS-ES=LF-EF When a task has zero slack it is critical and lies on the critical path for that network configuration. Watch these tasks carefully for a delay here will delay the entire project.