Any process or project can be defined as a set or series of activities that need to be carried out in order to complete that process. These activities have dependences, based on which a network of activities can be made. The longest path in duration, amongst the paths in the network, from start to end of the process, is known as the Critical Path, and the activities that make up the critical path are known as critical activities.
Critical Path Method, commonly known as CPM, is a project scheduling technique used for effective project management. In this method, a project model is constructed that includes:
- Work breakdown structure or the list of interdependent activities of the project
- The specific duration or time value allocated to each activity
- Dependencies between the activities
Importance of CPM
This project scheduling method tells us:
- When the entire process or project will be completed, i.e. the project duration,
- Which activities in the project are critical, i.e. any delay in those activities can potentially delay the whole project
- Which activities in the project are non-critical, i.e. activities that can be late without affecting the project duration, thus providing the project a flexibility
- Finding project status on any given date, based on schedule and budget
- To identify, if there are enough resources that the project requires
- And, finally if the project duration has to be reduced, what is the best possible way that gives us the least additional cost
Steps to come up with Critical Path Method for an activity
Step 1: Make the WBS (Work break-down structure) or identify the activities that form the project, and their respective durations.
Step 2: Establish an activity sequence, clearly identifying which activity precedes which ones, and what activities can be completed simultaneously.
Step 3: Develop the network diagram. Project network is basically making a WBS of the project, modelled to represent the precedence of activities, where the arcs represent the precedence and the nodes represent the activities
For example: Nodes represent activities A and B, and the arrow represents the precedence of the activities, where the activity B can start after the completion of activity A.
Similarly, when calculating the LF (late finish) times, the LF of an activity is the minimum of all the following activities’ LS (late start) times, as an activity can latest finish only before the first following activity starts. For example: In the previous example, calculating the ES, EF, LS, LF, and slack.
Step 4: Identifying the critical path:
For this step we need to determine following four time factors for each activity:
- Earliest Start Time (ES): The earliest an activity can start once all the predecessor activities are over
- Earliest Finish Time (EF) = ES + Activity Duration
- Latest Finish Time (LF): The latest an activity can finish that ensure project completion on time
- Latest Start Time (LS) = LF – Activity Duration
Based on these parameters, activity slack can be calculated
Slack = LS- ES = LF-EF
If Activity Slack = 0, the activity is a critical activity, otherwise it is a non-critical activity.
Please note that for calculating ES (early start) of an activity, we take the maximum of the predecessor activities’ EF (early finish) time, as an activity can start the earliest only when all the predecessor activities end.
Since, the activities A, D, H, I, K, L have slack =0, these activities are Critical Activities.
Hence, Critical Path for this project is A-D-H-I-K-L.
Step 5: Calculate the project duration, based on the duration of Critical Path, by adding the duration of the critical activities.
For instance, in the project taken in previous example, the project duration is the sum of the times of activities A, D, H, I, K and L.
Project duration = 3+5+1+6+5+2 = 22 days
Step 6: Update the network diagram throughout the project implementation process based on the actual project progress to refine the activity and project predictions.
The critical path method is an incredibly common and powerful tool used across the garment industry today. But it’s only as powerful as the data entered into it— estimations are off, if resources aren’t calculated correctly, the entire project may fail. Take ample time to to identify the critical activities of the project, in the project planning phase.