# PROJECT MANAGEMENT Network or Critical Path by pptfiles

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```									   PROJECT MANAGEMENT
Network or Critical Path Analysis
IB BUSINSS & MANAGEMENT –
A COURSE COMPANION (p238-p291)
Network or Critical Path Analysis
• Network or Critical path analysis was designed
to help project managers plan complex
projects that have multiple interrelated tasks.
• It is a mathematical tool.
• It can be a great help in breaking down a
complicated production process into clearly
manageable units.
What is the aim of
Critical Path Analysis?
• The aim is to identify which tasks are so
“critical” that they cannot be altered without
having an impact on how long it tasks to
complete the whole process
OR
by extension the likely effect of a change in
any inputs such as HR or finance.
What do we need to know to create a
network diagram?
• The number and order of tasks
• The dependencies of each task (which one
cannot be started until another has finished)
• The time that each task takes.
Conventions
• The process is drawn starting on the left of the
page and working towards the right.
• A task is identified by a start and a finish that
looks like the figure below.
CONVENTIONS
• A task is shown by drawing a line
between the two nodes.
• We put the code for the task above
the line and the duration below it.
This is shown below.
CONVENTIONS
• More than one task can start at the same node
as shown in figure 5.23
• More than one task can finish as the same node
as shown in figure 5.24
This means that task B cannot start
until Task A has been completed.

This means that neither task B nor C
can start until task A has been
completed.

This means that task C cannot start
completed.

This means that that neither task C
nor D can start until task A and B
have been completed.
DIAGRAMS YOU CANNOT DRAW

Drawing a diagram like this is not allowed as the
task starting at the same time may have different
durations so they cannot finish at the same node
too. In this case there has to be at least a
different start or finish node for the tasks.
CALCULATIONS
Each mode is split into different quadrants. This is
because we can fill these in with numbers that show the
starting time and finishing time of the task and these will
depend on what comes before the task, how long that
Understanding Calculations
• Every task has two nodes attached that will look like the figure below.
• The very first node on the diagram – the start of the whole process always has an EST
and LFT of 0.
• The very last node in the diagram has as EST and LFT equal to the total duration of the
whole project. Again the two numbers will always be the same.
• We calculate the ESTs by working from left to right and finding when is the earliest
time that we can start each task in the process.
• We calculate the LFTs, by working from right to left and finding out when is the latest
time each task can be finished by.
Example 1
• Imagine it is the last lesson of the school day.
• The teacher won’t let you go until you have
finished your work and the class has tidied up.
Code       Task          Preceded by   Duration (Minutes)
A          Finish Work   -             30
B          Tidy Up       A             7
Example 2
• Now imagine that the teacher says, that after finishing your work, some of
you should tidy up and the rest push away the laptops.
• After tidying up, those students should put all the chairs on top of the
desks.
• Nobody can leave until all tasks are completed.

by
A        Finish Work                     -          30
B        Tidy Up                         A          7
C        Put away laptops                A          15
D        Put chairs on top of desks.     B          6
Example 2
At node 1, it will be zero, node
2 will be 30 and node 3 will be
37 (30 + 7) minutes. However,
for node 4 we have to make a
decision. We can’t leave the
school until both tasks C and D
have been completed. So the
rule is that when there is more
than one task at a node the EST
always takes the higher
number.
In this case the EST for node
will be 45 (30 + 15 > 37 + 6)

As with our earlier example,
we work from node 4 for
our LFTs. They will start at
45 and then node 3 will be
39 (45-6) but again when we
have a node at which there
is more than one LFT we
must make a decision. We
take the lowest number.
So for node 2, the LFT will
be 30 (because 45-15 < (is
less than) 39-70
• We can distinguish between a task that is critical
(that cannot be altered without affecting the
• We can show the critical path, which is all the
affecting the whole process – by adding these
symbols.
• Note: All critical tasks will have ESTs equal to their
LFTs.
FLOATS
• Spare time is known as a float and is
important because it may be useful to know
how much time a task can be delayed without
having an impact on the whole process.
• There are two main floats.
Free Float
Total Float
Free Float
• This is the amount of time a task can be delayed
without having an impact on the following task.
It is calculated by the following formula:
EST of next task – duration of the task – EST of this
Total Float
• This is the amount of a time a sequence of tasks
can be delayed without having an impact on the
whole process.
It is calculated by the following formula:
Total Float vs Free Float
• As the total float is for the whole process and
the free float immediately effects the next
activity alone, the total float will always be at
least the same as the free float and often
times it will be a bigger number.
Total Float ≥ Free Float
Float - Example
Code    Task                         Preceded by   Duration (minutes)
A       Finish Work                  0             0
B       Tidy Up                      0             2
C       Put Away Laptops             0             0
D       Put Chairs on top of Desks   2             2

• Critical Tasks always have 0 floats
• Task B, cannot be delayed as long as the next task (D) starts
after 37 minutes; that is directly after the task has been
completed.
• But also if we were to delay task B by two minutes this would
delay everyone leaving school.
• Task D, cannot be delayed by more than two minutes as this
will affect the whole process as it is the last activity.

• Sometimes it is necessary to
include in the network a task that
is doe not actually exist.
• It is needed though to make sure
that the whole process is
completed logical.
• Imagine that the teacher decides that the
students putting away the laptops must sing
their favorite pop songs as they do it.
• Remember when drawing the network we
can’t have two tasks taking the same time
starting and finishing from the same nodes.
• So we will have to another intermediate node
in the network.
Example – Dummy & Variable Task
(Table)
(minutes)

A       Finish Work                  -             30
B       Tidy Up                      A             7
C       Put Away laptops             A             15
D       Put Chairs on Top of Desks   B             6
E       Sing Pop Songs               A             15
• As the task does not physically exist we cannot
allocate time to it – its duration is therefore
zero and we need not put this on to the
network.
• The task is shown by a dotted line – with the
arrow to show the direction necessary.
• The EST for the task following it will be EST
start + 0 = EST start.
• The point of the network diagram is to show
those tasks that are so critical the manager has to
focus on them as any delay will have an
immediate impact. Critical paths therefore have
some important characteristics
 They must have EST equal to LFT at the start and
finish nodes.
 They must therefore have zero floats.
 They cannot be altered without affecting the
whole process.
What are the benefits of critical path
analysis for project managers?
• By distinguishing between critical and non-critical
focus attention.
• The manager can calculate the effect of diverting
resources from non-critical activities to critical
ones and so reduce the overall time of the whole
process.
• The manager can factor into calculations, the
effect of delays to specific tasks and the impact
on the whole process.
What are the benefits of critical path
analysis for project managers?
• The manager can also cost the various tasks
and so be able to calculate the most efficient
funding for the process.
• This is very important for complex projects
that may require funding over a long period of
time.
• The manager can therefore determine an
effective cash flow for the whole process and
identify critical points in the whole process
What are the benefits of critical path
analysis for project managers?
• The manager can test crash the process to see
the effect of a change in circumstances.
• There are many computer programs that can
run the process for speedy calculations.
Limitations of Critical Path Analysis
• Critical path analysis focuses only on quantitative data and
it ignores the qualitative aspects of production.
• It can be confusing to create the network diagram,
especially if dummy activities are required.
• The assumption is that all activities are sequential with a
definite start and end to the whole process.