-: The project evaluation and review technique,
referred to as PERT, is very powerful
but can be a bit confusing.
In this clip, we will go through
the first step in PERT,
which is to draw a network diagram.
There're two PERT diagram formats
that can be used.
Activity on arrow format
where the activities and times are written
along the arrows between the nodes.
And activity on node format
where the activities are represented
in the nodes or shapes of the diagram,
and the times are written along the arrows.
For this example, we're going to use
the activity on node format
and map out a small renovation project.
The information needed for constructing our PERT diagram
is the list of project activities
and also, the column of preceding activities.
These are the activities that must be completed
before you can start the activity that is listed.
You need to remember to not just look at the numbers.
There're good reasons why you can't start
one activity before finishing another.
Think about this project.
You can't lay a new floor slab
before you have excavated
and removed the existing floor.
It just can't be done.
And you wouldn't be able to build a new toilet
until you have removed the old toilet block.
To draw our diagram, we are going
to work through the list of activities step by step.
So first, we will draw a Start and End node.
Then, we identify the first activity.
We do this by looking for any activity
that does not have a preceding activity.
In this case it is remove the kitchen,
which is activity one.
So we draw an activity node for activity one
in our diagram, and then we draw an arrow
from the Start node to activity one.
We now consider activity two,
which is remove the toilet block.
The preceding activity for this is activity one
so the arrow will move from one to two.
The third activity to consider
is excavate the floor for the new slab.
The preceding activity is activity two,
so our arrow will move from two to three.
The next activity is activity four,
remove the mezzanine,
which has the same preceding activity
as activity three,
that is they both stem from activity two.
This means that the path has now split.
So we will draw an arrow from activity two
to activity four.
Activity five follows on from activity four
so we continue drawing the arrow
from activity four to activity five.
Now things can start to get a little confusing.
Activity six is to lay the new slab
and it is not dependent on activities four and five.
It is actually dependent on activity three,
and so we need to make sure
that we enter this on the correct path.
We need to find activity three,
and then draw the arrow from there
to activity six.
Activity seven, build toilets,
is dependent on activity six
so we draw the arrow from six to seven.
Activity eight is to fit out the toilets.
This activity occurs after activity seven is completed
so we draw the arrow from seven through to eight.
Once again, we need to be careful
because activity nine is dependent on activity six,
not on seven and eight.
And if we get this wrong,
we will confuse the paths.
So we need to find activity six,
and draw the arrow from there to activity nine.
We're now really close to finishing this drawing.
So we need to look at activity 10,
fit out the kitchen, with its preceding activity
as activity nine.
So the arrow is drawn from activity nine
to activity 10, and we have now completed
the review of all activities
and we have three paths.
We need to complete these paths
by linking up the final activities
on each path to the End node,
that is activities 8, 10, and 5.
Now that we have completed the diagram
we will be able to move on to calculate
the estimated times for the activities
and the project's critical path.