01 · Purpose
Why and when to use it
Why?
It prevents a schedule from assuming that dependent work can start before its prerequisites are ready.
When?
Use it when several workstreams interact or when the completion date depends on the sequence of activities.
Who takes part? The leader develops the network with the people doing the work and validates external dependencies with their owners.
02 · Application
How to apply it
Start with: Activities derived from the WBS, dependency rules, estimated durations and assumptions about resource availability.
- List the activities needed to produce each work package.
- For each activity, identify its genuine predecessors.
- Draw the relationships and check for missing links or circular logic.
- Estimate durations in consistent units.
- Calculate earliest finishes and trace the longest-duration path.
- Review resource limits and uncertainty before converting the network into calendar dates.
03 · Example
A warehouse dispatch project
Original illustrative example. All quantities, targets, roles and timings below are fictional teaching assumptions, not findings from a real project.
| Activity | Duration | Predecessor | Earliest finish |
|---|---|---|---|
| A: approve measure definitions | 2 working days | None | Day 2 |
| B: collect observations | 5 working days | A | Day 7 |
| C: validate data extract | 3 working days | A | Day 5 |
| D: produce baseline report | 2 working days | B and C | Day 9 |
04 · Interpretation
What the result tells you
The longest path is A → B → D: 2 + 5 + 2 = 9 days. C finishes two days before D can start, so it has two days of total float in this simplified network. This assumes activities start as early as possible and required resources are available.
Completion check: An activity network with logical links, duration assumptions and the current controlling path.
05 · Judgement
Mistakes and limitations
Common mistakes
- Adding dependencies only because activities appear next to each other in a list.
- Calling the most expensive activity the critical activity.
- Ignoring resource conflicts or treating estimated duration as certain.
Limits of the tool
The critical path can change as durations and constraints change. Resource availability may extend the schedule beyond the dependency-only calculation; complex networks require explicit scheduling methods.
07 · Reading
Sources and further reading
Toolset backbone: Six Sigma+Lean Toolset: Mindset for Successful Implementation of Improvement Projects, second edition, edited by Stephan Lunau, with Renata Meran, Alexander John, Olin Roenpage and Christian Staudter (Springer, 2013). This reference identifies the toolset; the book text was not available for a chapter-level comparison in this development pass. The explanations, application sequence and fictional examples here are original LeanTrainingLab teaching material. Linked readings provide background; they do not prescribe every example or target.