9. Viewing the Project’s Critical Path
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 in this context 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 changing task relationships
or durations, 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.
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 days. 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. One way to see the critical path is to switch to the
Detail Gantt view.
In this exercise, you view the project’s critical path.
-
On the View tab, in the
Task Views group, click the
down arrow below the Gantt
Chart button and then click More Views.
-
In the More Views dialog
box, select Detail Gantt, and
then click Apply.
The project appears in the Detail Gantt view. -
On the View tab, in the
Zoom group, click Entire Project.
Because of the highly sequential nature of the task
relationships in this project plan, almost all the tasks are on
the critical path, and in the Detail Gantt view, their Gantt bars
are formatted in red.
Notice the Gantt bar of task 41, Review with
author. 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.) -
On the View tab, in the
Task Views group, click the
down arrow below the Gantt
Chart button and then 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.
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 File tab, click Options, and in the Project Options dialog
box, click the Advanced tab. In the Tasks Are Critical If Slack Is
Less Than Or Equal To box, enter the number of days you want. In
this same dialog box, you can elect to display multiple critical
paths. -
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. -
You can toggle the formatting of critical tasks and slack
directly in any Gantt Chart view. On the Format tab, in the Bar
Styles group, select or clear the Critical Tasks and Slack check
boxes.
Tip
To learn more about managing a critical path, click the Help
button (which looks like a question mark) in the upper-right corner
of the Project window, and in the Help Search box, type
critical path.
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