When assigning resources to an activity in Primavera P6, there are several resource assignment settings that should be taken into consideration. The resource assignment calculation settings in User Preferences will affect how the duration, units, and units/time for the activity are spread as additional resources are added. These calculation settings can be adjusted from the by selecting Edit > User Preferences.

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The settings for resource and role assignments can be found under the Calculations tab.

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Under Resource Assignments, we are given two options that will apply when adding or removing multiple resource assignments to an activity:

  • Preserve the Units, Duration, and Units/Time for existing assignments, or

     

  • Recalculate the Units, Duration and Units/Time for existing assignments based on the activity Duration Type

In this article, we will compare what each of these settings does and how it affects the resources and activities in the schedule.

Preserve the Units, Duration, and Units/Time for existing assignments

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I’ll start by keeping Preserve the Units, Duration, and Units/Time for existing assignments selected.

In my schedule, I have only just begun assigning resources to activities. My activity Install Underground Footings has a duration of 5 days and will need to utilize several resources. I’ll start by assigning my first resource by selecting Add Resource from the Resources tab in the Details section.

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First, I’ll assign a labor resource, Bill Anderson, to this activity by selecting him from the list and selecting Assign.

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Bill Anderson has a standard units/time of 8 hours per day, and was automatically given full work for the activity’s duration of 5 days. This gives him a total of 40 hours, or units, for this activity.

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I’ll add additional resources to this activity the same way, by selecting the Add Resource button. I’ll assign another labor resource, Robert Smith, to this activity as well.

Robert Smith also works 8 hours/day, and he was also set to work all 5 days of the activity’s duration. Altogether, he was also given a total of 40 units for this activity.

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This is what will happen when you choose to Preserve the units, duration and unit/time for existing assignments: another assignment will be added to the activity with the same budgeted units – assuming the new resource is working the same amount of time as the previous resource. Instead of minimizing the units, durations and units/time needed for the activity as more resources are added, they will all stay fixed to the activity. We are simply adding more resources, without taking away the amount of time or units needed for the activity to be completed. With more resources added, of course, the actual units and durations spent on this activity could be lessened – but with this setting, we are not assuming that this will happen.

Now, let’s take a look at what happens when you choose to have this data recalculated instead. Before I change the settings, I’m going to delete the second Robert Smith assignment from this activity.

I’ll return to the User Preferences window by selecting Edit > User Preferences. Once again, I’ll select the Calculations tab.

Recalculate the data for existing assignments based on the activity Duration type

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This time, I’ll choose to Recalculate the data for existing assignments based on the activity Duration type.

Because this option will recalculate the resource assignment data based on Duration type, you may want to modify the activity’s current duration type. This can be done from the General tab of the Details section.

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There are four options available for Duration Type:

  • Fixed Duration & Units,

     

  • Fixed Duration and Units/Time,
  • Fixed Units, and

     

  • Fixed Units/Time.

When additional resources are assigned to activities, the data will be recalculated – but the duration type allows us to choose which activity data to stay fixed. Any non fixed data will automatically be recalculated as resource assignments are made.

We’ll take a look at what happens as we add resources to the activity with each of these different Duration types.

Fixed Duration & Units

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Fixed Duration & Units should be used when the duration and the amount of the resources are known and supposed to remain fixed in the schedule. This will keep the duration of the activity and units needed to complete it fixed even as additional resources are added to the schedule. This is the recommended duration type to use for time and budget constrained projects.

Returning to the Resources tab, I’ll assign Robert Smith to this activity again.

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With the Duration and Units fixed, the activity’s duration has stayed at 5 days and the units needed for completion have stayed at 40 hours. However, because I added an additional resource to the activity, the units have been evenly split between both resources. Each resource is now working a total of 20 hours to complete this activity. As for their units/time, each resource is now working only 4 hours a day, as less hours were needed to complete the activity’s work. The budgeted units for the activity stayed the same, but the resource units were minimized as additional resources were assigned to work.

Fixed Duration and Units/Time

 

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Fixed Duration and Units/Time will keep the duration of the activity and the resource’s units/time fixed. This duration type is best used for activities that are supposed to be completed within a certain, fixed time frame, regardless of how many resources will be assigned to the activity. For Task Dependent activities, this duration type is most often used.

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After assigning another resource to the activity, the duration has remained fixed at 5 days. The Units/Time for each Resource has remained fixed at 8 hours/day. With these two fields fixed, both resources are once again working 40 hours overall. This essentially gives us the same result as if we had chosen to Preserve the Units, Duration, and Units/Time for existing assignments. Although the resources Units are not fixed, because the activity duration is stuck at 5 days and their Units/Time is set to 8 hours/day, both resources will still be working 40 hours overall. Although not fixed, the Units have remained the same in this circumstance.

Fixed Units

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Fixed Units will keep the Units for the activity fixed, even as additional resources are assigned. This duration type is best used for activities where the amount of work that needs to be completed is fixed and resource dependent. Essentially, as additional resources are added to the activity, the duration will decrease – more hands on deck means that the work can be completed faster.

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After assigning another resource to the activity, the total units needed for the activity has remained fixed at 40 – but now, those units are split evenly between the two resources. Both resources are still working at 8 hours/day, which in turn decreases the activity’s duration from 5 days to 3 days. With the units fixed, the assigned resources are now sharing the overall work that needs to be completed, allowing the activity to finish in less time than originally planned.

Fixed Units/Time

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Fixed Units/Time will fix the units/time needed for the activity to be completed.This duration type is supposed to be used when the user would like the resource units per time to remain unchanged while the activity duration or units change. If you have an activity, for example, that uses machinery that requires two workers to operate, Fixed Units/Time might be the right choice. This type is most often used if the user uses resource-dependent activities.

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After assigning another resource to the activity, each resource is fixed at working 8 hours/day – but now, they are both working only 20 units each. Just like with the fixed units, this option also has decreased the duration to 3 days. Again, with more hands working on the activity, the activity is able to be completed at a faster rate.

Summary

Whether you choose to Preserve the Units, Duration, and Units/Time for existing assignments or Recalculate the data for existing assignments based on the activity Duration type depends on your needs within the project. I personally prefer to use the Preserve option, as it allows me to avoid incurring any errors while making additional resource assignments. However, if you are working with activities that are task-dependent and have a fixed amount of work that needs to be done, you may want to choose to Recalculate the data and consider how adding more resources can shorten the duration of the activity. Additionally, if you are dealing with resource overallocation, you may want to Recalculate the data and experiment with how adding additional resources can help minimize this.

If you have any comments, questions or suggestions, please use the comment section on the bottom of this page, and don’t forget to subscribe to our blog to get more Primavera P6 tips & tricks directly in your inbox!

Lauren Hecker is a Primavera P6 Professional trainer and teaches Onsite and virtual Primavera P6 Professional courses. To see her next open enrollment course, please visit our calendar. To schedule an onsite or custom course, please contact us!

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