Fixed work, Fixed Duration, Fixed Units explained

In last blog we understood the task type and how they related, Please read same before continuing below and remember the formula !

Duration x Units = Work

Use Fixed Work when you know the amount of work, In this case you can change the duration to stretch out or compress the time you allow to get that fixed amount of work done. Changing work changes duration proportionately, but changing duration does not change work.

Suppose you set fixed-work task to have 40 hours of work. Duration is automatically set to 5 days (by default 8 hrs./day) . Now if you change the duration to 10 days , the work will still remain as 40 hrs (Fixed work) and task changes: from 8 hours/day (the default) to 4 hours/day (units changes).

Other hand for Fixed Duration task the Duration remains constant, for example you have fixed-duration task set to 5 days. Work will automatically be set to 40 hours (by default calculation). Now if you change the work to 20 days the task changes: from 8 hours/day (the default) to 4 hours/day.(units changes)
Use Fixed Duration when you think about a task in terms of how much time you want to allocate for it irrespective of work and units.

Use fixed-units, when you think of tasks interchangeably in terms of its work and the time allocated for it. That's generally because, when you do assign resources to the task, you expect they will work on the task a fixed number of hours (i.e. units) of their time each day. So, changing either the work or the duration will change the other one proportionally.

Below table is quick cheat sheet to remember  the relationship .

Quick Cheat : Relationship between Work, Unit and Duration

Understanding Duration, Work and Units

Remember,

Duration x Units = Work

Fixed Units suggests that are the amount of capacity that a resource can devote to a task. An example of this is that you suggest to Microsoft Project that a resource can only work 50% of the time on a specific task. Microsoft Project will then automatically calculate the duration of the task with the resource only working 50% of the time.

Fixed Duration suggested that the task the task must be completed within a given duration. As you assign a single or multiple resources to the task, Microsoft Project will automatically calculate the appropriate resource allocation percentage to ensure the task is completed within the given duration.

Fixed Work suggests that a task has a specific numbers of hours work associated with it. In this scenario, we know that the task is going to take ten hours to complete. We have the ability to schedule the tasks overall duration for five days with fixed work of ten hours. Assuming a single resource is responsible for completing the task, Microsoft Project will schedule the resource to work two hours a day for the five day duration.