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Fixed units / Fixed work - best practice? RRS feed

  • Question

  • Hi,

    Have a Project that consists of mainly Fixed duration tasks, but it also includes some assembly tasks where we can use more staff if we need to finish the task earlier. Have tried to figure out wheter to use fixed units or fixed work for the assembly tasks, but are so far unable to decide which one to use. Both of them work just fine, but which is the proper one to use, and which is the most commonly used type, fixed units or fixed work?

    Say that we have an assembly task that requires 100 hours of work, and we have 2 Resources working on it and it takes 50 hours duration to complete it. Then we notice that it will require 130 hours of work so we add a third resource so we can complete it on time. Does it really matter if we use fixed units or fixed work on these kind of tasks? We have Control of the plan with either one of them as Project asks if the duration or amount of units/work should be changed so there is really not a big deal, but would still like to know which of them that is the most common one to use?

    Kind regards //Anders

    Monday, August 25, 2014 8:52 AM

Answers

  • Let me further Trevors reply,

    First point of Industrial Modelling is not to follow the pack, just because someone else does something doesn't make it correct. Understand the software and the situation you are modelling and select the best option. To do this it is critical to understand the 5 options.

    1.Fixed Units/Effort Driven On
        As more resources are added: the duration will decrease, Work remains, All resources working full time
    2.Fixed Units/Effort Driven Off
        As more resources are added: the duration remain, Work increases, All resources working full time
    3.Fixed Duration/Effort Driven On
        As more resources are added: the duration remain, Work decreases, All resources working PART time
    4.Fixed Duration/Effort Driven Off
        As more resources are added: the duration remain, Work increases, All resources working full time
    5.Fixed Work/Effort Driven On
        As more resources are added: the duration remain, Work increases, All resources working full time

    Now to answer your question, THE DIFFERENCE BETWEEN 1 AND 5 IS WHEN YOU CHANGE THE DURATION fixed work (1) will keep the amount of work constant and change how many hours the men/woman work each day to complete the task as scheduled. Compareded to fixed units (5) when the amount of work will increase or decrease to match the duration.

    If you not changing the duration it does not matter which one you use. Although, I recommend (5) as it will have the resources allocated at 100% (Probably most realistic) but you have a better understanding of the situation and can make a better call.

    • Marked as answer by AT_lamnea Thursday, August 28, 2014 8:47 PM
    Thursday, August 28, 2014 3:21 AM

All replies

  • The two settings which work in combination are the task type and effort driven. There are three task types and effort driven can be turned on or off. That makes 3 x 2 possible combinations, except fixed work only always has effort driven on, so that means there are only 5 possible combinations of the two settings and each has a different result.

    So it is not a matter of which is the most common to use. What matters is that you set them so that you get what you intended when you do whatever it is that you do. If you get it wrong the first time you only have 4 other possible combinations to try. In your example, you want the duration to stay fixed while you add the other resource and increase the . So set the task to fixed duration, say effort driven is either on or off, assign the third resource. MSP will assign the resource at 100% which will make the work increase to 150 hours. Then tune down the assignment % for that resource until work is 130 hours (use the assign resources dialog). Or else, use the task usage view to type in the 30 hours on whatever days it occurs.

    If you can't make that work, you may have had the wrong effort driven setting so go back and start again with it set to the other.

    It is handy to have the details displayed in the split lower pane while you do this. Display details and right click on the blank space and choose work.

    Hope this helps

    Monday, August 25, 2014 11:03 AM
  • Hi again Trevor and thank's a lot for your reply, it was very helpful. Based on that we enter both the amount of work required and the duration when we initially set up the tasks would you recommend any of the various task types?

    For example: When we plan we estimate that the required work is 300 hours and the duration is 150 hours. We will most certainly change one or the other of these values during the time when the task is ongoing. However it is very seldom that we change the units, if duration needs to become 100 hours we just add a resource, if the work takes longer time we extend the duration accordingly leaving the Resources as they are.

    Kind regards //Anders

    Monday, August 25, 2014 11:25 AM
  • Let me further Trevors reply,

    First point of Industrial Modelling is not to follow the pack, just because someone else does something doesn't make it correct. Understand the software and the situation you are modelling and select the best option. To do this it is critical to understand the 5 options.

    1.Fixed Units/Effort Driven On
        As more resources are added: the duration will decrease, Work remains, All resources working full time
    2.Fixed Units/Effort Driven Off
        As more resources are added: the duration remain, Work increases, All resources working full time
    3.Fixed Duration/Effort Driven On
        As more resources are added: the duration remain, Work decreases, All resources working PART time
    4.Fixed Duration/Effort Driven Off
        As more resources are added: the duration remain, Work increases, All resources working full time
    5.Fixed Work/Effort Driven On
        As more resources are added: the duration remain, Work increases, All resources working full time

    Now to answer your question, THE DIFFERENCE BETWEEN 1 AND 5 IS WHEN YOU CHANGE THE DURATION fixed work (1) will keep the amount of work constant and change how many hours the men/woman work each day to complete the task as scheduled. Compareded to fixed units (5) when the amount of work will increase or decrease to match the duration.

    If you not changing the duration it does not matter which one you use. Although, I recommend (5) as it will have the resources allocated at 100% (Probably most realistic) but you have a better understanding of the situation and can make a better call.

    • Marked as answer by AT_lamnea Thursday, August 28, 2014 8:47 PM
    Thursday, August 28, 2014 3:21 AM
  • Mark, thank you. This was a simple and clear explanation. It is Fixed work with effort driven we should use.

    Kind regards //Anders

    Thursday, August 28, 2014 8:47 PM