# PERT and critical path

A PERT chart shows activities and dependencies as a network rather than as bars, which makes the critical path visible: the sequence with no slack, where any delay is a delay to the whole project.

It is the diagram to draw when someone asks what would actually happen if a task slipped.

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## When to reach for one

* Schedule risk analysis before committing to a date.
* Explaining why one task matters more than three others.
* Comparing plans, where the critical path differs between options.

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## How to draw it in Capable

| **Route** | **Use when**                                                 |
| --------- | ------------------------------------------------------------ |
| Graphviz  | Networks with automatic layout, which suits activity graphs. |
| draw.io   | Annotated versions with durations and slack marked.          |

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## A worked example

Activities, durations, and a critical path in bold:

![PERT and critical path](https://help.gocapable.com/images/att1418395687.svg)

The source, which you can paste into a new diagram and edit:

```
digraph pert {
  rankdir=LR;
  node [shape=box, fontname="Helvetica"];
  edge [fontname="Helvetica", fontsize=10];
  start [shape=circle, label="Start"];
  end [shape=doublecircle, label="End"];

  start -> design [label="5d"];
  design -> build [label="15d", penwidth=3];
  design -> content [label="8d"];
  build -> test [label="10d", penwidth=3];
  content -> test [label="2d"];
  test -> launch [label="3d", penwidth=3];
  launch -> end;
}
```

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## A few things that catch people out

* Slack is the useful number. Tasks with slack can absorb delay; tasks without cannot.
* The critical path moves when estimates change. Recalculate rather than trusting last month's diagram.
* Three-point estimates (optimistic, likely, pessimistic) are the original point of PERT and still useful.

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## Related

[Work breakdown structureDeliverables decomposed until they are estimable.](https://help.gocapable.com/diagrams/work-breakdown-structure.html)

[Gantt chartTasks, dependencies and a critical date.](https://help.gocapable.com/diagrams/gantt-chart.html)

[ExamplesWorking diagrams you can copy.](https://help.gocapable.com/diagrams/examples.html)

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_A plan you can change is a plan people trust._