Have a weird issue with project durations

Reducing Units Method
If I have a task that takes 4 days (set up using defaults) - If I reduce the persons units to that task to 50% - the duration increases to 8 days - no problem with this.

Calendar assignment method
However I have a separate calendar for PT time staff - who only work 4 hours.If I assign this task to someone using this calendar the duration does not increase (although the end date moves)

To a simple guy like me- I appear to be doing the same thing - as effectivley the hours per day are reduced from 8 to 4 in either scenario. - can anyone provide me with an explanation as to why the duration doesn't increase when I use the different calendar ?

Actually the math does work, but I agree - it's confusing :-)

Duration = Work/ (units * hours per day)

So, the first scenario:

8 days = 32 hours/(8 hours per day * 50%)

Second scenarion:

4 days = 32 hours/(8 hours per day * 100%)

I hope this helps.

Thank you Julie,

But in the second scenario the person is only working 4 hours per day not 8. In my humble opinon it should revise the duration to 8 days

8d X 4h = 32 hours

But the definition of a day is set only once in File > Options, Schedule - hours per day.

When you work with resources with different schedules, using "duration" stops being helpful. I usually suggest people just talk Work, Start and Finish dates.

Thank you.

That makes sense........sort of !

You're welcome and thanks for the feedback.