Last month we started to have a look at more detailed
facilities that Project provides to help us to examine and fine tune our
projects. This month we’ll begin looking into the assignment of multiple
In Microsoft Project: Lesson 5—Working With Resources I
commented that resource assignment can be very complicated. My advice is, if at
all possible, keep to one resource per task and it is difficult to go wrong or
fail to understand what’s going on. Remember, and I repeat: Effort-driven
scheduling only takes effect when resources are added to or removed from a task.
So, after the first assignment of a resource, effort driven scheduling has no
effect unless you subsequently add or remove resources from the task.
So what happens if we assign more than one resource to a task? Project is an
effort driven program. This is defined as a scheduling
method that bases a task's duration on the amount of work the task requires and
the number of resource units assigned to it: i.e., calculation is based on the
Resource Units X Duration = Work
The values in the formula are set up for each task when a resource
is first assigned; subsequent changes will be governed by the
formula. There are several places in Project where you assign resources, but
with multiple resources on one task you need a view that shows all the relevant
To illustrate this best, I always recommend using the split screen technique
as in the following example. Let's have a project to make a garden with an
initial plan that includes a pool of Gardeners. In a new project starting on 1
Mar 04, create a 10 day task: Make Terraces, then select it and then Window/Split.
You will see in the lower pane all the details we need to get the
assignments right, i.e. the task Name and its Duration. There is
the Effort driven selection (default is checked ON) and the Task type (default is Fixed Units) of
which more later. On the left you can also see fields for the Resource Name,
the Units assigned and the Work.
Click in the Resource Names cell and enter "Gardeners" and
click OK (activating the OK button turns it and the adjacent button into Previous and Next to allow progression through the tasks.) You will see
that Project assumes you want one full time gardener (100%) and for the Duration
of 10 days it will consume 80 hours of Work (based on the default 8 hour
day or 40 hour week).
Now, let's say it's going to take too long at 10 days, and to speed it
up we assign another Gardener from our pool. So, change the Units value
to 200% and click OK. Note that against the Gantt bar, the number of
resources assigned is placed after the resource name if the Units are
other than 100%. As this task is Effort Driven, the effort (Work)
remains the same at 80 hours and thus Project reduces the Duration to 5
days - mission accomplished.
Play around with assigning more Gardeners and see the Duration reduce
each time, and try less than 100%, say 50% meaning a Gardener only works half
time per day (i.e. 4 hours per day, and thus to achieve 80 hours work, the Duration
goes out to 20 days.) OK, changing the number of Units using the same
resources from a pool is quite straight forward and works as one might expect
with effort driven tasks. Restore the Units to 100% and the Duration
should still read 10 days.
Fred from next door is a keen gardener and offers to help out. Click in the
next Resource Name cell under the Gardeners and type in Fred and
As you would expect the Duration again halves as they now both share
the work: 40 hours each.
Suppose the task was still taking too long and you decide to add another
Gardener. Click on the Gardeners’ Units and increase to 200% and OK.
You will see no change to the amount of work and the Duration doesn't
change as you would have hoped. What has happened to the effort driven formula
now? Well, you’ve presented Project with problem it cannot answer without
guidance from you. It still upholds the 80 hours of work, but each Gardener is
now only doing 20 hours whilst poor Fred slaves on for his original 40 hours.
Thus, Fred becomes the driving resource as he still needs 5 days to finish. Try
adding more and more Gardeners – the Duration remains the same based on
Fred’s assignment. Equally, if you put in one gardener working half time (50%),
the Duration goes back to 10 days, as that resource becomes the driving
resource. (Remember always to click the OK button whenever you’re happy
with the changes in order to get Project to calculate the new data. When you
do, the buttons change to Previous and Next to allow you to
progress through the tasks.)
You can see that blindly adding resources to a multi-resourced task my not
achieve the reduction in Duration you want. You have to engage brain and
be selective in your choice of resource assignment.
Now let’s try a different assignment. Remove Fred and assign 200% to
Gardeners and ensure the Duration is 5 days with 80 hours Work.
Now reassign Fred.
The Work is assigned equally between the 3 resources at 26.67%
(Project rounds to 2 decimal places, though the real value is used in
calculations) each, reducing the Duration to 3.33 days. Try
experimenting with these assignments and try adding Mary and Joe, and also a
material resource like Bricks, until you run out of explanation of why Project
calculates as it does. Isn’t it easy to get into a mess!
In real life I have two prime tips:
· Always use the split screen technique when you have more than one
resource to assign so that you can see all the elements and the resulting
calculations that Project makes.
· If you run
into problems, delete all the assignments from the task, reset the Duration
and reassign them all to read what you want before you click the OK
button: this in effect becomes the first assignment to that task and
thus the effort driven formula will not come into effect until you click
I hope you will experiment with assigning resources in this way until you
understand what is happening or, at least, be able to recover from any
misplaced assignments. Next month we’ll have a look getting Project to do what
you want with the assignments by seeing the effect of removing the effort
driven setting and changing the Task Type.