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PROJECTSCHEDULINGTOOLS ANDTECHNIQUES 117

Figure 10: Gantt chart for software launch project in Microsoft Project.

float. Slack or float is the amount of time an activity may

be delayed without delaying a succeeding activity or the

project finish date.

To find the critical path for a project, a project manager

should first develop a good network diagram, which, in

turn, requires a good activity list based on the WBS. Once

a project network diagram has been created, the manager

must also estimate the duration of each activity to de-

termine the critical path. Calculating the critical path in-

volves adding the durations for all activities on each path

through the project network diagram. The longest path is

the critical path.

Figure 11 provides an example of a project network

diagram using the activity-on-arrow format for simplicity.

Note that each of the four paths starts at the first node

(1) and ends at the last node (8) on this diagram. This

figure also shows the length or total duration of each path

through the project network diagram. These lengths are

computed by adding the durations of each activity on the

path. Because path B-E-H-J at 16 days has the longest

duration, it is the critical path for the project.

Figure 12 shows the network diagram and critical

path when the same project information is entered into

Microsoft Project 2000. This format is called the prece-

dence diagramming method (PDM) and is used by most

software packages. Project management software can

definitely help in creating network diagrams and deter-

mining critical paths and slack amounts for all project

tasks.

What does the critical path really mean? The critical

path shows the shortest time in which a project can be

completed. Even though the critical path is the longest

path, it represents the shortest time it takes to complete

a project. If one or more of the activities on the critical

path takes longer than planned,the whole project schedule

G=6

C=3

Note: Assume all durations are in days.

Path 1: A-D-H-J Length = 1+4+6+3 = 14 days

Path 2: B-E-H-J Length = 2+5+6+3 = 16 days

Path 3: B-F-J Length = 2+4+3 = 9 days

Path 4: C-G-I-J Length = 3+6+2+3 = 14 days

Since the critical path is the longest path through the network diagram, Path 2,

B-E-H-J, is the critical path for Project X.

B=2 F=4 J=3

H=6

I=2

A=1

D=4

E=5

2

(^13)
4
5
6 8
7
Figure 11: Using a project network diagram to determine the
critical path.