CPM (Critical Path Method)- in Software Project Management - Software Engineering - By Sandeep Singh

Critical Path Analysis – Interactive Case Study + CPM Diagram

See activities A–H as a network diagram, then explore forward pass, backward pass, float and the critical path.

Activity‑on‑Node diagram

Forward & backward pass

Float and critical path

Step‑by‑Step Simulation (A–H)

Use the steps and the CPM diagram to understand how the critical path F → G controls the project duration.

1 Activities & rules

2 Forward pass (ES/EF)

3 Backward pass (LS/LF)

4 Float & critical path

These are the activities, durations, and precedents for the project.

Activity	Duration (weeks)	Precedents

Network rules: one start node, one end node, no loops, no dangles, time flows left to right, and each node stores ES, EF, LS, LF, and Float.

Forward pass: calculate earliest start (ES) and earliest finish (EF) for each activity.

Act	Dur	ES	EF	Precedents

Click “Run forward pass” to show earliest times along each path (including F→G path).

Backward pass: calculate latest start (LS) and latest finish (LF) without delaying the project end.

Act	Dur	LS	LF	Precedents

Click “Run backward pass” to see latest times working back from project finish.

Float shows how much an activity can slip without delaying the whole project. Zero float ⇒ critical.

Act	Dur	ES	EF	LS	LF	Float

Critical path

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Project duration

–

Critical activities count

–

After you click “Calculate float & highlight critical path”, the critical activities will glow and appear here.

Real‑World Use of Critical Path

The Critical Path Method (CPM) finds the longest chain of dependent tasks that defines the minimum project duration.

Project scheduling

ES / EF / LS / LF

Float / Slack

Apollo Project (1969)

The Apollo program used critical path ideas to track thousands of engineering, testing, and training tasks so the Moon landing occurred on time and under tight budget control.

Panama Canal Expansion (2016)

The canal expansion relied on CPM to coordinate locks, excavation, and infrastructure among many contractors, keeping the opening date realistic.

London Olympics (2012)

Olympic venues, transport projects, and supplier work streams were planned with critical paths so that the Games could start with all key facilities ready.

Activity‑on‑Node CPM Diagram

This picture shows how activities A–H connect. Critical activities (zero float) will glow green after calculation.

Normal activity node

Critical activity node

Arrow = “must follow” relation

Tip: First click “Run forward pass” and “Run backward pass”, then “Calculate float & highlight critical path” to see F and G become critical on the diagram.

In this case study, activities F and G have zero float, so F → G is the critical path that fixes the total project duration.