I think a more important question is why do you want all the tasks to be
Fixed Duration? IMHO, that is the LEAST common task type, pretty much
reserved for odd-ball situations like test that must run for 72 consecutive
hours, that sort of thing. Generally if a resource works harder on a task
(higher assignment percentage) the time it takes to do the task should
shrink. Or conversly if the number of man-hours of work the task should
require changes, the length of time it will take to do the task should also
change in step with it. Fixed Duration will disable both of those
behaviours. Expressed in everyday language, Fixed Duration translates into
"No matter how hard or how little we work and no matter how much work we
have to do, how much deliverable we have to make, this task will take
exactly the same pre-determined length of time to finish." Not many things
in the real world work like that. In my more cynical moments I tend to
think people used Fixed Duration to try to force the schedule to look like
what senior management wants it to look like instead of looking like what
the laws of physics dictate it WILL actually behave like when you're down in
the trenches doing the work. Management wants 100 widgets to be done in a
week and it takes a widget maker 4 hours to make one - no problem, I'll just
have the one widget maker on staff work 48 hour work-days for the next week.
Fixed Units is to me the most logical default task type with Fixed Work a
close second. Usually the amount of work required is directly related to
the amount of deliverable that must be produced. We have 400 square feet of
wall to paint and the painter is physically capable of doing 10 square feet
per hour. The task will require 40 man-hours of work, period, end of story.
He will work as hard as he will work, no faster, no slower. The amount of
wall to paint is fixed in granite, thus so is the work at 40 man-hours, no
more, no less. So either Fixed Units or Fixed Work make the most sense. If
we realize that the square footage is 300 feet, what is going to change when
we bring our esitmates into line with reality, the speed the painter works?
Nope, it's the time it will take him to complete the wall. Task should be
Fixed Units, the work should be edited, and the duration should change.
When the painter tells us his boss says he also has to work in the room
across the hall at the same time as in our room so he's only going to be
able to devote 50% of his effort to our task, does that mean the room shrunk
and the man-hours required has gotten less? Nope, he still has to do the
same amount of Work but now he's working slower - duration must change.
Task is Fixed Work. Since tasks are ALWAYS physical actions extending over
time producing an exact required amount of deliverable, the physical
behaviours of most tasks in most projects resembles one of those two
scenarios. I repeat, legitimately Fixed Duration tasks are incredibly rare
in the real physical world.
