Understand and Manipulate the Critical Path in MS Project

September 1, 2009 | Author: PM Hut | Filed under: Computer Based Information Systems, Critical Path

Understand and Manipulate the Critical Path in MS Project
By Peter Kolevas

Understanding the critical path in MS project can be a relatively daunting task. In order to do this you need to have a fundamental understanding of the predecessor relationships you have setup on the tasks within the plan.

First thing to do when determining the critical path on the project is to ensure that every task in the project has a predecessor, with the exception of summary tasks and the first task in the project. To do this determine the mandatory logic throughout the project first, and then move into your discretionary logic. Once complete you will have a plan that you can work with to understand the critical path.

In order to view the critical path in MS Project I recommend doing 2 things:

  • Display the critical path on the Gantt chart.
    1. Right click on the open space in the Gantt Chart.
    2. Select Gantt Chart Wizard.
    3. Move through the wizard selecting the critical path options.
  • Display the Total Slack column on the Gantt table.

Once complete, any task with 0 days in the Total Slack column is considered critical since it has no slack or ability to slip until it impacts the end date of your project. All the tasks with 0 slack on them should also be red in the Gantt chart.

Any task with a number >0 should be blue on the Gantt chart and for the purposes of MS Project is considered not critical.

Now there are a few things to review since the critical path is exposed.

  • Does your discretionary logic make sense? Do you have too many dependencies on tasks due to this logic? If so tweak the plan.
  • Does your discretionary logic cause too many tasks to become critical? Should you rearrange some logic to make the critical path make more sense? If so tweak the plan.
  • Are there any tasks with large amounts of time in the Total Slack Column? If so, is the logic on that task appropriate, or did you miss that task when creating the logical network. If so tweak the plan.

Once you have reviewed and are comfortable with the schedule network you can manipulate the way in which MS Project shows the critical path. First why would you do this?

  • An example would be that there are a few tasks that are not critical but only have 1 or 2 days of slack. You may want to show these tasks as critical to management.
  • Another example would be tasks that are near critical above, but have resource constraints that make you concerned such as a key resource that may leave.
  • A third example would be to influence behavior for a resource on that task. Once a resource realizes their task is not on the critical path, they tend to think they have more time and begin to procrastinate. Procrastination on a task that has slack will eventually eat that slack and steal it from other tasks. This is what I like to call “Stealing Float” ex. Testers hate it when developers steal the float and they end up with no slack to test.

To manipulate the way in which MS project calculates the critical path, open the Tools>>Options menu, click on the Calculation tab, and increase the number of days in the option “Tasks are critical if tasks are less than or equal to”. When you move back to the Gantt chart tasks that meet this criterion will now be red and considered critical to MS Project.

Peter runs http://petekolevas.com, a blog on smart techniques for managing projects.

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1 person has left a comment

Pete,

I like the article and agree with your suggestions. I help people get to grips with Microsoft Project and explaining the concept of the Critical Path calculation is always fun, especially when you explain that the good news is that the tool does all the number crunching but that it is useful to understand the concept.

I suggest to my “victims” that a good schedule should have a series of Top Level Summary Tasks and Milestones to conclude each section/stage/phase of the project. I advise against linking tasks because you can but then state that in my mind every single TASK with 2 exceptions should have @ least 1 predecessor and 1 successor, most people “get” what the exceptions are. I then suggest creating a custom combination view, I call it the LOGIC View (Gantt Chart on top,Relationship Diagram on the bottom) to help people “cycle” their way through the schedule - this approach can eliminate what I call “loose end” or “orphan” tasks and will result in their Total Slack being significantly reduced, again most people get this in terms of getting tasks done sooner rather than later. It also fits in with the notion of managing stage boundaries which is a PRINCE2 concept that is actually a good practical idea.

Dominic Moss wrote on November 2, 2009 - 12:04 pm | Visit Link

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