June 12, 2011, 2:55 p.m.
posted by arthur
A critical path is the series of tasks that will push out the project’s end date if the tasks are delayed. The word critical has nothing to do with how important these tasks are to the overall project. It refers only to how their scheduling will affect the project’s finish date; however, the project finish date is of great importance in most projects. If you want to shorten the duration of a project to bring in the finish date, you must begin by shortening (also referred to as “crashing”) the critical path.
Over the life of a project, the project’s critical path is likely to change from time to time as tasks are completed ahead of or behind schedule. Schedule changes, such as assigning resources to tasks, can also alter the critical path. After a task on the critical path is completed, it is no longer critical because it cannot affect the project finish date. In Chapter 15, “Getting Your Project Back on Track,” you will work with a variety of techniques to shorten a project’s overall duration.
A key to understanding the critical path is to understand slack, also known as float. There are two types of slack: free and total. Free slack is the amount of time a task can be delayed before it delays another task. Total slack is the amount of time a task can be delayed before it delays the completion of the project.
A task is on the critical path if its total slack is less than a certain amount-by default, if it is zero. In contrast, noncritical tasks have slack, meaning they can start or finish earlier or later within their slack time without affecting the completion date of a project.
In this exercise, you view the project’s critical path. One way to see the critical path is to switch to the Detail Gantt view.
1. On the View menu, click More Views.
2. In the More Views dialog box, select Detail Gantt, and then click the Apply button.
The project appears in the Detail Gantt view.
3. On the Edit menu, click Go To.
is the keyboard shortcut for Go To.
4. In the ID box, type 12, and then click OK.
The Scene 3 tasks and later tasks are critical tasks. In the Detail Gantt view, Project distinguishes between critical and noncritical tasks. Critical task bars are red, but noncritical task bars are blue. In this view, you can also see tasks with free slack.
Notice the Gantt bar of task 18, Scene 7-process dailies. The blue bar represents the duration of the task. The thin teal line and the number next to it represent free slack for this task. As you can see, this particular task has some slack and is therefore a noncritical task. (Remember that the term critical in this sense has nothing to do with the task’s importance, but only with how much or little total slack is associated with the task-and, ultimately, what effect the task has on the project’s finish date.) The slack on task 18 was caused by the Start No Earlier Than constraint applied to task 20. Without that constraint being applied, all tasks in the project would have been critical.
5. On the View menu, click Gantt Chart.
Working with the critical path is the most important way to manage a project’s overall duration. In later exercises, you will make adjustments that might extend the project’s duration. Checking the project’s critical path and, when necessary, shortening the overall project duration are important project management skills.
“Critical path” is a frequently misused phrase on many projects. Just listen for references to critical path work on your current projects to determine how frequently the phrase is used correctly. Remember that critical has nothing to do with the relative importance of a task, but only with its effect on the project finish date.
Here are a few other things to keep in mind when working with the critical path:
By default, Project defines a task as critical if it has zero slack. However, you can change the amount of slack required for a task to be considered critical. You might do this, for example, if you wanted to more easily identify tasks that were within one or two days of affecting the project’s finish date. On the Tools menu, click Options, and in the Options dialog box, click the Calculation tab. In the Tasks Are Critical If Slack Is Less Than Or Equal To box, enter the number of days you want.
Project constantly recalculates the critical path even if you never display it.
You see free slack represented in the chart portion of the Detail Gantt view, and you can also see the values of free and total slack in the Schedule table. You can apply the Schedule table to any Gantt Chart or Task Sheet view.
To learn more about managing a critical path, type critical path into the Search box in the upper right corner of the Project window. The Search box initially contains the text Type a question for help.