Scott Button - 2010-10-27

The software appears to be changing the durations that I enter.

It probably IS changing your durations, if you are changing the resource assignments.

By default, MS Project uses Fixed Units, with Effort Driven checked.

This means that if you add or remove resources, MS Project will keep the units fixed, and modify the duration so that the total units remain the same.

For fixed-unit tasks:
a. If you revise units in a fixed-unit task, Microsoft Project recalculates duration.
b. If you revise duration, Microsoft Project recalculates work.
c. If you revise the amount of work, Microsoft Project recalculates the duration.

Set the task to Fixed Duration if you want the task duration to remain constant, regardless of any change in assignment units or work for the task.