We already know that network analysis helps the project manager in estimating the time of completion of the project and represents the logical interrelation among activities. Some of the network techniques are as follows:
- PERT – Programme Evaluation and Review Technique
- CPM – Critical Path Method
- RAMS – Resource Allocation and Multi-project Scheduling
- PEP – Programme Evolution Procedure
- COPAC – Critical Operating Production Allocation Control
- MAP – Manpower Allocation Procedure
- RPSM – Resource Planning and Scheduling Method
- LCS – Least Cost Scheduling
- MOSS – Multi-Operation Scheduling System
- PCS – Project Control System
- GERT – Graphical Evaluation Review Technique
Critical Path Method (CPM)
The Critical Path Method or CPM technique was developed by an American company in the year 1957. Its employees required this type of technique to plan the closure, repair and restart of the chemical plants. This project was complex and involved numerous tasks.
After its success in the company, the Critical Path Method or CPM was applied to agricultural and construction projects to establish logical sequencing of the project activities. The applications of CPM are spreading in almost all industries including the software industry. A critical path establishes a clear order of the activities to be performed for a certain period.
CPM is an algorithm used for planning, managing, analysing and controlling the timing of a project. It helps to identify critical and non-critical activities of the project from start to end of the project and saves the project from risks of delay and wastage of resources.
The critical tasks involved in project management require control and timely analysis of risks. If the duration of these tasks changes, then it will have a direct effect on the completion of the remaining activities of the project and it will prolong the duration of the project.
The critical path of a project can be constructed in MS Excel using Gantt charts. The visual representation of activities and their dependencies streamlines the project stages in an effective manner.
Steps for Construction of Critical Path Method
The construction of Critical Path Method involves the following steps:
Identification of activities
In this step, the project is divided into various activities, number or letters are assigned to each activity to identify them. The activities should have a specific duration and date of completion assigned to them.
Identification of sequence of the activities
After identification of activities and assigning the name or number to each one of them, a proper sequence or order is fixed for the activities. This helps in knowing the dependencies of the activities and establishing interrelationship between them.
Construction of network of activities
Once the project activities are assigned a sequence, a network is established or a network diagram is drawn by interconnecting the activities. A network diagram or a path analysis chart is created after finding the dependencies of the activities. An arrow is used to identify the dependencies of the activities.
Determination of the time intervals for completing each activity
In this step, the estimation of time to undertake each activity is derived. Through this step, the total time duration in completing the whole project is identified.
Finding a critical path
This is the last step of CPM. The construction of critical path reveals the longest path to complete the project. The step uses the following parameters:
- Early Start: It represents the time when all previous tasks to start the project are completed.
- Early Finish: It represents the nearest start time and the time duration to complete the activities of the project.
- Late Finish: It represents completion of all the activities without postponing the deadlines.
- Late Start: It represents the time after deducting the last end time to complete the activity.
Important Terms, Notations and Formulae
Let us discuss some of the common terminologies used in Critical path Method or CPM.
Activity Time and Activity Scheduling
The activity time is the estimated time taken for the completion of an activity. For example, 15 days will be taken for construction of walls of the first floor of the house. Activity scheduling is the sequence of activities to be performed and the time taken by each activity to be completed.
Each activity is estimated, managed and controlled to maintain the quality of the project. This helps in the final scheduling of the project to estimate the project start and end date.
The total float determines the amount of time for which an activity can be delayed without delaying the overall project duration. It is also known as “float” or “slack”.
The free float is calculated by deducting the early finish of the activity from the early start of the successor activity of the network diagram of the project. It represents the amount of time for which a scheduled activity can be delayed without delaying the early start date of an immediate successor activity. Free float is thus calculated based on last activity in an activity sequence.
Independent float is a part of the total float. In the independent float, an activity that can be delayed for start without affecting the time duration of the preceding activities is represented. The formula for the calculation of total float is as follows: Independent Float = Total Float – Tail Event float
The critical events are the series of activities that can be identified by calculating the correlation between the project parameters like project duration and project cost. These events are also known as critical chain of events.
These are the activities of the project that must start and finish on time so that the project completes on the estimated end date or the deadline. A delay in these activities will delay the entire project.
The critical path is the longest path to complete the project. It includes a series of critical activities to complete the project. These activities must start and end by a certain time. This path of critical activities determines the end date or the deadline of the project and is thus close managed.