It sounds like your sequence of events might be that you originally defined
Mary in the resource sheet with an 8 hours calendar and a max allocation of
100%. You assigned her to a 5 day task at 100%. Her work thus is 40 hours.
Now you said you changed her to be working 50% but it sounds like you did so
by adjusting her max allocation on the resource sheet down to 50%. That has
NOT changed any of her assignments, it only changed a: the default level for
new assignments, and b: the level that will be considered over-allocated
when exceeded. You'll need to explicitly edit her assignment percentage on
each individual task to change her work assignments.
When you do, think about it a bit before making the change so you get the
edit done correctly. You say her work should drop from 40 hours to 20 hours
and you're right enough in that a 5 day task at 50% is 20 hours. But is
that really an appropriate adjustment for this particular task? When you
estimated original duration that task you estimated it would take 5 days to
get a certain required amount of output, say 1000 widgets assembled.
Regardless of how many hours a day Mary now puts into it, the task usually
will still require 1000 widgets before it's done. If 1000 widgets took 40
man-hours to build then, doesn't it make sense that 1000 widgets will still
take 40 man-hours of work to create now? So when you adjust Mary's
committment to the task from 100% to 50%, shouldn't the work stay at 40
man-hours but the duration increase from 5 to 10 days? If she only works 5
days at 50%, she'll only build 500 widgets and your project will fail
because that deliverable isn't finished. Of course, it could be that you
only need 500 widgets after all. That's why there's the Task Type setting
.... if you still need 1000 widget set the task to Fixed Work and when you
change her assigment to 50% the work will stay at 40 and the duration will
go to 10. If you really only need 500 widgets, but don't need it done
sooner than 5 days even so, set it to Fixed Duration before editing and the
duration will remain at 5 while the work will drop to 20.
Some people suggest adjusting calendars to reflect lower than full workday
hours. I don't care much for that appoach myself. I think the calndar
should reflect when they're physically present and able to work, their
actual workday. If they're a full-time person that usually would be an 8
hours day. If we can only have them for 4 hours a day, setting their max
allocation at 50% means we can use them up to 4 of those 8 hours but we're
not going to try to micromanage theiur day for them. If you have to juggle
4 hours of project related work with 4 hours of non-project work, which is
what the 50% of an 8 hour calendar implies, you're perfectly capable of
organizing your day yourself. It usually won;t matter to me if you do your
4 hours in the morning, the afternoon, or interleaved throughout the day -
as PM I'm only concerned with the bottom line final result. OTOH, if the
resource is a part-time employee working a 4 hour a day afternoon shift, it
is important for me to know when they're going to be there. Thus I'd create
a calendar that has their part-time hours of work and if I was going to use
them 4 hours a day I'd assign them 100%, NOT 50%. The percentage is the
percentage of their calendar, not of the firm's business day.
