The critical path is a sequence of tasks that enables the completion of an archival project in the shortest possible time. It encompasses the duration from project start to completion and identifies which tasks must be finished before others can follow.
While some tasks can be sequenced with much flexibility, critical path tasks are confined to task relationships.
The critical path is imperative when project costs are significant because scrupulous scheduling can ensure that the committed work days are as low as possible. Although learning about the Critical Path Method (CPM) can be overwhelming for archivists new to taking on project leadership roles, becoming familiar with the strategy increases project success in an environment in which every penny counts.
CPM Methodology Background
The CPM was created in the 1950s by DuPont to schedule renovations to its chemical plants. This technique uses a diagramming method called activity on node and creates the project schedule based on the longest path through the network. To show relationships between tasks, you draw arrows from predecessor to successor.
The CPM employs several definitions, which include:
- Duration: Number of work days, excluding holidays or other nonworking days, required to complete an activity.
- Forward Pass: A strategy to develop early start and early finish dates for each task, starting at the beginning and progressing to the end.
- Backward Pass: A method to gauge late start and late finish dates by starting at project completion, using finish times and working in reverse.
- Float or Slack: The latest point a task may be postponed from its earliest start date without delaying the project finish date.
- Early Start Date: The earliest point an action can begin, based on any schedule constraints.
- Early Finish Date: The earliest time the activity can finish.
- Late Start Date: The latest point that the action may begin without delaying the activity’s successor.
- Late Finish Date: The latest point a task may be completed without hindering the activity’s successor.
Slackers, Forward Passes, Backward Passes, Oh My!
Determining the free and total slack for each activity helps archival project managers make schedule trade-offs. Free slack or free float is the amount of time an action can be postponed without delaying the early start of any following activities. The early start date for an action is the earliest possible time an activity can start. Total slack or total float is the amount of time a task may be deferred from its early start without delaying the planned project finish date.
You calculate free slack and total slack by performing a forward and backward pass through the project. A forward pass establishes the early start and early finish dates for each activity. The early finish date for an action is the earliest possible time an activity can finish. The project start date is equivalent to the early start date for the first network activity. Early start plus the duration of the first activity is equal to the early finish date of the first activity. It is also equal to the early start date of each subsequent activity. When an activity has multiple predecessors, its early start date is the latest of the early finish dates of those predecessors.
A backward pass determines the late start and late finish dates for each activity. The late start date for an action is the latest possible time an activity might begin without delaying the project finish date. The late finish date for an activity is the latest possible time a task can be completed without impeding the project finish date.
Crashing the Party
If the finish date is more important than the budget, spending money to shorten the schedule is an option; this is called “crashing”. A common crashing technique is adding more workers to a task. This approach is useful when used in a limited way. If you add too many workers, the project slows as people get in each other’s way. Other options include paying for overtime, paying rush fees for faster delivery of materials, or paying for people with higher rates, who can hopefully complete work more quickly.
Like any technique for shortening the schedule, the tasks you want to crash are on the critical path because they are the ones that determine the duration of the project. First, look for the longest tasks on the critical path. Crashing can increase the risk of those tasks which is why the number of crash tasks should be kept to a minimum. Crashing one long task duration might cut all the time you need out of the schedule. By crashing longer tasks, you can crash fewer of them. After you have crashing candidates, evaluate those tasks to find the most cost-effective ones.
The Path to Success
While some archival projects may not necessitate the detailed use of the Critical Path Method, mapping out a project from start to finish allows archivists to see how they can best use their time and resources. Doing so allows archival project managers to modify the project schedule in relation to the real-world challenges they face in archival repositories.
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