Working with seasoned project managers, schedulers, and countless students in my Microsoft Project classes, I see a lot of people focusing heavily on the critical path and how the tasks on it drive business decisions. However, it is also important to know how to evaluate what is not on the critical path and how to take a look at available slack time. This knowledge can help you figure out when following the critical path might be at risk; in some cases, before the project has even started.
## Show Critical Gantt Bars
In Project 2010, to display the critical path go to the **Format** tab, click the **Critical Tasks** checkbox.
Notice that throughout the schedule, critical tasks are marked with red Gantt bars and non-critical tasks remain blue.
## Show Free and Total Slack Fields
In Project 2010, to display additional fields do the following:
1. On the **Format** tab, in the Columns group, click the **Insert Column** button and select **Total Slack**.
2. Repeat and select **Free Slack**.
3. Drag the columns to their desired location.
Notice that all critical tasks for this schedule display
0 in the Total Slack column.
This follows the traditional definition of a Critical Task that you may have seen from PMI or Advisicon materials – when the earliest date a task can start is equal to the latest date a task can start, the task is considered critical because its available delay time is zero days (i.e., 0 days of slack time). Critical tasks must stay on schedule to honor the project end date.
## What Free Slack Tells Us
Notice that in the Tradeshow Promotion portion of the schedule all of the tasks have Total Slack, but a few also have free slack.
If the only column you pay attention to is total slack and you delay some of these tasks to free up resources for critical tasks, you may not realize that other non-critical tasks in the schedule will also shift.
The advantage of Free Slack is this informs you of the number of days of slack time that are available to you where nothing else in the schedule will shift; such as a successor task. Best practice when delaying tasks to correct for a situation (e.g., resource shortage) in your schedule is to delay the less risky tasks which have free slack.
## What Negative Total Slack Tells Us
A very valuable situation to project managers is when Total Slack displays a value that is less than zero (negative).
This seems like an impossible situation since critical tasks are at zero, you may be wondering what a negative value means. In Microsoft Project, a negative Total Slack is an indicator of a missed deadline. If that task – or even the entire project – has not started, this schedule is already in trouble. This is an excellent time to work with the resource manager, sponsor, team or others to get the schedule back on track to avoid the missed deadline.
## Some Takeaways
* Next time you are evaluating your schedule and making a decision about which non-critical tasks to delay in order to free up a resource, consider choosing the tasks with Free Slack first and delay within the Free Slack value to keep the rest of the schedule the same.
* If you use deadlines, display the Critical Path with Total Slack to discover when tasks are already scheduled to be late and make adjustments before you reach that point in the schedule.
I hope you found this information useful. For more information on scheduling and Advisicon best practices, please sign up for an upcoming course in [Managing Projects with Microsoft Project 2010](http://managing-projects-with-microsoft-project-2010-cl.eventbrite.com “Register for the public “Managing Projects with Microsoft Project 2010” course”).
*[PMI]: Project Management Institute