The Critical Path Method

The Critical Path Method (CPM) is a technique for identifying the time-critical activities of a project.

These identified activities are often (rightly) given a lot of attention. Be it to guarantee the timely completion of the project or to take corrective measures in case of a delay.

So much for the theory, but how do we get there and what do we do with it?

Some history and background: The critical path method was developed back in the late 1950s by Messrs Morgan R. Walker and E. Kelley, Jr. It can be applied to all kinds of projects, be it software development, product development, space projects to the most ordinary private house building. Any project that has dependencies between activities can use this method.

How do I get to my critical path?

There are only five steps required to identify the critical path.

  1. define each activity
  2. establish dependencies
  3. estimate the duration of the activities
  4. draw a network diagram
  5. calculate (which path of dependent activities takes the longest?)

Once point 5 is done and all possible paths have been calculated, I have identified the critical path. That’s it.

With the appropriate software, point 4 is not necessary, and point 5 is also carried out automatically by many planning programmes. Steps 1-3, however, require intensive consideration and elaboration. Briefly on these three points:

Defining the individual activities can be done in various ways, but I prefer to proceed from rough to fine. This means nothing other than identifying the major activities (or more extensive delivery packages) of the project and then breaking them down to individual, manageable activities (e.g. <10 days duration). The method of working and presentation is up to you: Outline, table, mind map or large, small and very small slips of paper, whatever suits you best.

There will certainly be dependencies between these defined activities. You may now identify and document these. What does this mean?

  • pick an activity (any activity)
  • which activity (or several activities) must be completed before I can start the one I have chosen?
  • which activity can start as soon as I have finished the current one?
  • which activity can run in parallel with the selected one?

In addition to defining the dependencies, you now estimate for each activity the expected time to complete the activity. I will not go into the different estimation methods here. Use your personal experience, expert knowledge, reference projects, estimating workshops, bought-in knowledge, etc.

Creating the network diagram and calculating the critical path should be done by a software product you trust. The critical path can usually be displayed by one click or by settings in the view options.

Critical path identified – what to do?

What was that again about the definition of the critical path? The critical path is the sequence of those activities that add up to the longest project duration and thus have a direct impact on the project end date if delayed.

Knowing the critical path in your project brings some weighty advantages:

  • any change in the completion of the activities on this critical path directly affects the project end date; these activities thus require special attention – but not unlimited attention, otherwise other activities will get out of hand (it will happen, I promise!);
  • the non-critical activities or paths have a so-called float; this means nothing more than a buffer they have compared to the critical path (if this buffer is used up, this can become the new critical path); activities on the critical path understandably have a float of zero;
  • If your software offers baselines and a comparison facility, use this regularly and compare the current plan with previous ones; trackable changes across multiple histories may allow you to predict trends in which activities may be on fire in the near future.

A plan is just a plan

Please keep in mind that any plan is just a plan. The estimates and dates are not set in stone, changes can occur at any time and throw the most beautiful plan off track. The critical path can also change during the course of a project – however, with its help you will have the opportunity to identify the activities that are most important for meeting the project deadline and to be able to act accordingly if necessary.

In a separate article, I discuss the topic of “optimising project duration“. If your schedule is not as relaxed as when you originally planned it, you may find a tip in the article mentioned.

The above lines are merely the basis for working with the critical path. There are numerous variations and further activities, but they would go beyond the scope of this article.


What is the relationship between the Critical Path Method (CPM) and CPM Hubert Hell GmbH?

Although the CPM in the company name does not stand for the Critical Path Method, a close connection cannot be denied. Like the critical path, we do not lose sight of the essentials in our projects and our customer assignments:

  • we follow a golden thread
  • we know where the priorities lie
  • we have our sights clearly set on the goal
  • and maintain a relaxed and confident overview in the midst of all possible confusion.

So the CPM in our name could well stand for the Critical Path Method.

Curious now? Don’t believe it all? Then let’s talk about it.

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