Know the Basic Scheduling Formula
Duration = Work/Units
Understanding of the meaning of these three terms (See Project Help), as well as the formula itself, is key to understanding how Project schedules a task. To anyone who has changed any of these three parameters on a task, without understanding this formula, the changes that Project makes to the other parameter(s) can sometimes seem totally unexpected or bizarre.
Not knowing this formula is the biggest cause of frustration that people experience with the tool. Knowing the formula will not stop Project from doing things that you don’t expect, but it will allow you to know what changes to make so that it will do what you want.
Use Task Types correctly
What will Project do when you change either work, duration or units on a task – that is, which of the others will it change and which will it keep constant? The Task Type parameter is what tells Project how to behave. The general rule is:
If work, units or duration is fixed and you change one of the others, Project will recalculate the third, but wont change the one that’s “fixed”.
Even if you don’t set task type explicitly, each task defaults to one of the three – and the system default is “Fixed Units”. This can cause problems in many cases, because since most technical tasks are driven by the amount of work effort required, they should generally be “fixed work”
Understand the Effort Driven Task setting
If a task is effort driven, the total task work will remain the same if you add or remove resources. If you add a resource, the total amount of work effort will be divided among all of the resources, including the new ones, thereby reducing duration.
Good practice when adding resources to a task, even if you do understand this concept, is to explicitly specify the work and units for each assignment, so you remain in control of the division of labour. Do this in a usage view or the bottom half of a split-screen view.