Critical path analysis
This is the type of
diagram you are aiming
to draw
Network/critical path analysis
A decision making tool, used to plan
work flows
A complex tool, which organises work
to establish:
earliest start times
latest finishing times
the critical path
the float.
Aims of critical path analysis
To plan complex To identify critical
operations. activities – which
To identify when a are those activities
project must which must be
commence. completed.
To illustrate the To identify the float.
order of activities.
Nodes and activities
Activity
EST paint wall
EST
1 2
LFT Time LFT
3 hrs The arrow shows us
The node shows the
physical start and the actual task
which is being
finish of an activity
undertaken
Constructing the network
2 The
first job
1 2 4 Start the next activities
1 Start 3 Finish
the the job
project
Building a network
3
6 Start the next
1 2 5 Complete activity once
tasks 3 &4 both 3 & 4 are
complete
4
The completed diagram
7 Finish the job
3
1 2 5 6
4 Give each node a
number
Adding the information
Add the activities
and times
3
b c
a
3 hrs 7 hrs f
1 2 5 6
24 d e 3 hrs
hrs
3 hrs 4 2 hrs
The earliest start times
Add the earliest
start times
3 27
b c
a
f
1 0 2 24 3 hrs 7 hrs
5 34 6 37
24 d e 3 hrs
hrs
3 hrs 4 27 2 hrs
The latest finishing times
3 27
b 27 c
a
0 f
1 2 24 3 hrs 7 hrs
5 34 6 37
0 24 34 37
24 d e 3 hrs
hrs
3 hrs 4 27 2 hrs
32 Add the latest
finishing times
The critical path
*
* * 3 27
a
b 27 c
*
3 hrs 7 hrs f
1 0 2 24 5 34 37
0 24 34 6 37
24 d e 3 hrs
hrs
3 hrs 4 27 2 hrs Critical
32 activities are
a, b, c, f.
The float
With the network complete, you can now
identify any idle time.
This spare time is known as the float.
Resources can be allocated to other duties
during the float time.
In this activity there is only one critical time -
between tasks d and e, where there are 5
floating hours.
Float is calculated in a table of calculations.
The float table
Formula LFT – (EST - Duration)
Activity LFT EST Duration Float
What you will need
To undertake the analysis you will
need:
a list of activities
information on the order of tasks to be
completed
the time it takes to complete each task
any constraints on completing.
Starting the network
Before you can start the network,
you must create a table (task 4)
containing the following:
the activities in order
the time it takes to carry out
a letter for each activity.
You can then draw the network.