PERT

PERT (Program Evaluation and Review Technique) was introduced in 1957–1958 by the U.S. Navy for managing the Polaris submarine missile program.

It was developed by a Navy team working with Booz Allen Hamilton and Lockheed to handle the complex scheduling and uncertainty of large defense projects.

Key innovation: PERT introduced the idea of modeling a project as a network of activities with:

• Three time estimates for each task (optimistic, most likely, pessimistic)
• Statistical calculations to estimate the probable project duration and identify the critical path

Purpose: To manage projects where activity durations were uncertain, allowing better risk assessment and planning compared to traditional Gantt charts or fixed timelines.

Historical impact: PERT was one of the first formal project management tools and laid the foundation for modern project scheduling and risk analysis methods.

CPM

Critical Path Method (CPM) is a formal, mathematical approach to scheduling and optimising project timelines, in 1957 revolutionising how industries managed complex projects.

DuPont needed a systematic way to plan plant maintenance and construction projects, where delays in key tasks could hold up the entire project.

CPM was designed to identify the longest sequence of dependent tasks (the critical path) that determines the project’s minimum completion time and to identify float, helping managers see which tasks can be delayed without affecting the final deadline.

CPM was developed by James E. Kelley Jr. of Remington Rand and Morgan R. Walker of DuPont and first used in 1957.

PERT-CPM

PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method) are project management techniques used to plan, schedule, and control projects. Here are the fundamental principles of PERT-CPM:

The process

• Activity Identification - The project is broken down into specific activities or tasks required to complete it. Each activity is identified and defined in terms of its duration, dependencies, and resources needed.
• Sequence of Activities - The sequence in which activities must be performed is determined. Dependencies between activities are established to create a network diagram that depicts the logical order of tasks.
• Estimation of Activity Durations - Each activity's duration is estimated based on historical data, expert judgment, or other estimation techniques. Optimistic, pessimistic, and most likely time estimates may be used to calculate a weighted average duration.
• Critical Path Determination - The critical path, which represents the longest path through the project network, is identified. Activities on the critical path have zero slack or float and, therefore, directly impact the project's overall duration.
• Calculation of Earliest Start and Finish Times - Using the forward pass technique, the earliest start and finish times for each activity are calculated based on its dependencies and duration. This determines the earliest possible project completion time.
• Calculation of Latest Start and Finish Times - Using the backward pass technique, the latest start and finish times for each activity are calculated based on project constraints and the critical path. This helps identify activities with slack or float.
• Identification of Slack or Float - Slack or float refers to the amount of time an activity can be delayed without delaying the project's overall completion time. Activities on the critical path have zero slack, while non-critical activities have positive slack.
• Resource Allocation and Leveling - Resources required for each activity are identified, and resource constraints are considered during scheduling. Resource leveling may be performed to resolve resource conflicts and optimize resource utilization.
• Monitoring and Control - Progress is monitored against the project schedule to ensure that activities are being completed as planned. Any deviations from the schedule are identified, and corrective actions are taken to keep the project on track.
• Continuous Improvement - Lessons learned from project execution are documented and used to improve future project planning and execution. This iterative process helps refine estimates, optimize scheduling, and enhance overall project management practices.

By following these fundamental principles, PERT-CPM enables project managers to effectively plan, schedule, and manage projects, optimize resource utilization, and deliver projects on time and within budget.

CPM and Chronograph