Look again, that's not really true. Duration is the working time as defined
by its governing calendar between when the task starts and when it ends.
Fixed duration means that when you edit a resource assignment, the duration
won't change when you change either the work or the resource units. If you
have a task that takes 5 days duration, your "day" is defined as 8 hours,
and the calendar shows times 8am to 5pm for 8 hours a day, it wiull start
Mon at 8 and end Fri at 5. If you change the calendar to a 24 hour calendar
but leave everything else as is, the task will still show 5 days duration
but it will now start at 8am Mon and end Tue midnight - 40 clock hours
later. The task type won't effect that behavior.