Clarification on work, effort, duration relation

[Pat Kelecy]

I understand that Work = Effort (or Units) x Duration. So if one of these
is fixed, and a value is assigned to another, then the third can be uniquely
determined. Given this, I have the following questions:

1. What happens if the fixed quantity is changed? However does Project
recalculate the relation.

2. If a resource is not assigned, does Project assume a default value for
units?

Also, it seems more intuitive to make Work (number of man-hours required to
perform a task) the "scheduled" quantity, along with units, and let Project
compute duration, completion dates, etc. Then if you don't like how how
long things take, your only choice is to change units (add more resources or
work longer hours). I think this is the case for most work situations, but
for some reason most of the references I've looked at on MS Project assume
Duration is the scheduled quantity. Does anyone know what the rationale is
behind this?

Thanks for input. I appreciate it. -Pat

 

[Steve House]

When the fixed quantity is changed - Fixed duration, work is recalculated;
fixed units, duration is recalculated; and fixed work, duration is
recalculated.

As for what is estimated initially, duration is the normal course because
often you have a record of previous projects and duration is most easily
obtainable of the 3 variables - "Last year it took us 3 weeks to repaint the
office so this year it will probably be about the same..." If you have
man-hour estimates available, by all means use them if it gives you a better
planning strategy.

Steve House
MS Project MVP.

 

[Pat Kelecy]

Thanks Steve and Mike for the clarifications.

What I've noticed is that Work and Duration often get confused when talking
to people. When you ask someone "how long" it will take them to do a given
task, or even looking back at "how long" it took in the past, the response
is actually Work (hours or days expended doing the task) and not Duration
(or elapsed calendar time). At least that's been my experience (and it
becomes especially apparent when people start juggling several different
projects or tasks!). But as a PM that's really what you want to know,
particulary if your trying to estimate project costs (normally based on
hourly rates). Just my opinion .

Thanks again.

Pat

 

[Mike Glen]

You're welcome, Pat

Mike Glen
MS Project MVP

 

[Steve House]

Also be sure to remember Duration is NOT the same thing as Elapsed Calendar
Time unless you're talking about the working time calendar and not the
calendar on the wall or in your Day Timer. Assuming normal 8-5 work hours,
8am Mon to 5pm Fri is 105 elapsed hours but 40 duration hours.

Steve House
MS Project MVP