Finding the Best Tasks to Shorten
When a project schedule is too long, you want to rein it in with the
least amount of disruption to the work you’ve done so far. The critical path controls a project’s finish date, because it’s the longest sequence of tasks in a project. If the critical path gets delayed, so does the end of the project. (That’s why it’s called the critical path.) Because tasks on the critical path directly affect a project’s finish date, they’re the best candidates for shortening.
To find the critical path on your own, locate the task with the
latest finish date, and then trace back through its predecessors until
you reach the beginning of the project. Each task on the critical path
is called a critical task.
To be precise, the critical path is the longest sequence of tasks without any scheduling leeway (called slack time).
Slack time is the amount of time a task’s finish date can move without
affecting another part of the project. Free slack is how much a task
can move without affecting its successors. Total slack is the time a
task can move without affecting the end of the project. The lack of
slack time is the reason critical tasks affect a project’s finish. (If
you want insurance for your project’s finish date, you can add buffers
to your schedule. Then, if tasks delay, they eat into the buffers
instead of delaying the finish date, as described on Planning from the Top Down.)
Driving somewhere is a simple example of a critical path and slack
time. Suppose you and your brother are both heading to your elderly
Aunt Thelma’s for lunch, which starts at noon sharp. You’re taking the
highway, which takes 65 minutes. Your brother, on the other hand, is
driving his sports car over the scenic route, which is 90 minutes of
twists and turns. Your brother’s drive is the critical path, because it
takes the longest. That gives you 25 minutes of slack time before you
must start driving (or you can use the time to stop and pick flowers
for your dear auntie).
Once you start executing a project, you must keep close watch on the
critical path. Delays that occur in critical tasks directly affect the
project finish date.
Displaying the critical path in Project
The standard Gantt Chart view doesn’t show the critical path or
slack time initially. All you see are blue task bars. However, in
Project 2010, you can easily format the view to display the critical
path and slack time. Choose Format. In the Bar Styles section, turn on
the Critical Tasks checkbox and the Slack checkbox. The Gantt Chart
displays critical tasks in red and shows slack as narrow black bars at
the right end of task bars.
The critical path appears in red in the Tracking Gantt view (choose
Task→View, click the down arrow, and then choose Tracking Gantt) and
the Detail Gantt view (choose Task→View, click the down arrow,
choose→More Views, and then double-click Detail Gantt). The Tracking
Gantt view displays gray task bars for the baseline schedule, blue task
bars for noncritical tasks, and the Entry table in the table area. The
Detail Gantt view shows noncritical path task bars in blue and critical
path task bars in red along with the Delay table so you can evaluate
leveling delays.
Filtering the task list to show critical tasks
Filtering the task list to show only critical path tasks helps you
focus on shortening the tasks with the most bang for the buck. When you
use filters, you must reapply them regularly, like sunscreen, as the
box on The Ever-Changing Critical Path explains. To filter the task list to show only critical path tasks, do the following:
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Choose View→Data. Click the down arrow next to the filter box, and then choose Critical.
Project shows critical path tasks and the summary tasks to which they belong.
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To hide the summary tasks, choose Format→Show/Hide, and then turn off the Summary Tasks checkbox.
The summary tasks disappear, so you see only critical work package tasks.
Tip
Grouping by critical
status keeps noncritical tasks visible but out of the way. Click the
down arrow to the right of the Task Name column heading. In the
drop-down menu, choose “Group by”→Critical. Project lists all the
noncritical tasks first (under Critical: No), and then lists critical
tasks (under Critical: Yes). Revert to the regular order by
right-clicking the down arrow to the right of the Task Name column
heading and then choosing No Group.
Showing critical tasks in a Gantt Chart table
Bright red task bars in the timescale make the critical path easy to
see. But the tasks in the table area still look exactly the same.
Project has formatting features that can highlight the critical path in tables as well. If you want to see the critical path even in the Gantt Chart table area, do the following:
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To change the appearance of the table text for critical tasks, choose Format→Format→Text Styles.
The Text Styles dialog box opens. The advantage to formatting
text styles instead of individual text elements is that Project applies
the style whenever it’s appropriate. For example, if you modify the
appearance of text for critical tasks, then Project applies or removes
the formatting as tasks join or drop off the critical path, making it
easier for you to spot the changes.
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In the Item to Change drop-down list, choose Critical Tasks.
Any changes you make to the font or colors apply to all critical path tasks.
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Choose the font, font style, and font size.
The Font list displays the fonts installed on your computer. The
“Font style” list controls whether or not the text is bold or in
italics. The Size list includes the standard font sizes. (You can type
a number in the box to specify a font size not in the list.) Turn on
the Underline checkbox if you want the text underlined as well.
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Optionally, to change the font
color, in the Color drop-down list, choose the color you want (for
example, red to match the task bars).
Colors other than black can make text hard to read. If you do change
text color, opt for dark colors. In addition, remember that colors may
not reproduce well when you print in black and white. Consider yourself
warned.
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To highlight cells that use a text style, in the Background Color drop-down list, choose the color you want
.
For example, you can change the background for critical cells to red (shown as light gray highlighting in Figure 2). As you select options and settings, the Sample box previews the text appearance.
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Click OK.
Cells that use the text style immediately show the new
formatting. The background color and pattern apply to all critical task
cells, except for the Indicators column. These changes appear every
time you apply the current table. You can also create a custom table (Changing Table Contents) to show critical tasks in this way.
