Understanding Oracle Primavera P6 Duration Type Calculations
The P6 Duration Type works in conjunction with options set in the User Preferences, Calculations, Resource Assignments tab and becomes effective after a resource has been assigned to an activity.
Aim
The aim of this paper is to explain how the P6 Duration Type and the options set in the User Preferences, Calculations, Resource Assignments tab affect the resource assignment process and task resource calculations.
These options are useful to understand so when you change the duration of an activity you know if the crew size will remain the same or the work assigned to an activity will remain the same.
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Resource Assignments
The Calculations tab has two Resource Assignment options:
- Preserve the Units, Duration, and Units/Time for existing assignments. With this option, as Resources are added or deleted the total number of hours assigned to an activity increases or decreases. Each Resource’s hours are calculated independently.
- Recalculate the Units, Duration, and Units/Time for existing assignments based on the activity Duration Type. The total number of hours assigned to an activity will stay constant as second and subsequent resources are added or removed from an activity.
NOTE: This function does not work when the Activity Type is Fixed Duration and Units/Time.
The Recalculate the Units, Duration, and Units/Time for existing assignments based on the activity Duration Type function is similar to the Microsoft Project Effort Driven function and the Preserve the Units, Duration, and the Units/Time for existing assignments is the same as Non Effort Driven.
It is recommended that Preserve the Units, Duration, and Units/Time for existing assignments be used as a default as each individual resource assignment does not change as resources are added or removed from an activity.
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Duration Type
The Duration Type becomes effective after a resource has been assigned to an activity.
The Duration Type for all new activities is set in the Defaults tab in the Projects Window and all new activities are assigned this Duration Type.
The Duration Type for each new activity may be changed in the General tab in the Activities Window or by displaying the Duration Type column.
The Duration Type determines which of the following variables change when one of the others is changed in the equation:
- Resource Units = Resource Units per Time Period x Duration
For example, a 40-hour activity with 2 people working 8 hours per day will take 20 hours or 2.5 days:
- 40 hours of work = 2 people per hour x 20 hours
When an activity is in-progress this equation is modified to:
- Remaining Resource Units = Resource Units per Time period x Remaining Duration
Primavera has four options for Duration Type, Microsoft Project has three options.
The Primavera terminology that describes the way the software treats the relationship between Durations, Resource Units and Resource Units/Time Period is different from Microsoft Project and Elecosoft (Asta) Powerproject. Primavera has more options than all the other products and this gives the product more flexibility.
The table on the right should clarify these options.
Purposes of the Duration Types
Duration Type: Fixed Duration & Units
Purpose
- Option 1: This option is used when the Duration of an activity should not change when Resources are added or removed or Units/Time changed. For example, when the time to complete an activity is fixed, the resources may be manipulated until a satisfactory resource loading is established without the activity duration changing.
- Option 2: A change to the Duration will change the Units/Time; however, the Units will remain constant. If one person is assigned to an activity for 8 hours per day and the activity is doubled in duration, there will be now be one person working on the activity for 4 hours per day and the activity will require the same number of hours to complete.
IMPORTANT POINT: The Estimate at Completion WILL NOT change when the activity duration is changed and the number of resources WILL change.
Duration Type: Fixed Duration & Units/Time
Purpose
This Duration Type disables the User Preferences, Calculations tab option Recalculate the Units, Duration, and Units/Time for existing assignments based on the activity Duration Type.
- Option 1: This option is used when the Duration of an activity should not change when Resources are added or removed or Units/Time changed. For example, when the time to complete an activity is fixed, the resources may be manipulated until a satisfactory resource loading is established without the activity duration changing.
- Option 2: A change in the Duration will change the Units; however, the Units/Time will remain constant. For example, when there are two people assigned to an activity and the activity is increased in duration, there will still be two people working but for a longer period of time.
IMPORTANT POINT: The Estimate at Completion WILL change when the activity duration is changed and the number of resources WILL NOT change.
Duration Type: Fixed Units
Purpose
This option is used when the amount of work required to finish an activity is constant. For example, if there are 8,000 bricks to be laid and a bricklayer is able to lay 100 bricks per hour, there are 80 hours of work for one bricklayer, 40 hours for 2 bricklayers and 20 hours for 4 bricklayers. Changing the Duration or the Units/Time will not change the number of hours required to complete the activity.
Duration Type: Fixed Units/Time
Purpose
This option is used when the same number of people are required to complete an activity irrespective of the activity duration. For example, if a machine requires two people to operate it and therefore a Resource is assigned to the Activity at 200%, changing either the Units or the Duration will not change the Units/Time and there will always be two people operating the machine.
The duration of both Fixed Units and Fixed Units/Time activities will change if the resource Units/Time Period or Remaining Units are changed. It is the author’s preference to use:
- Fixed Duration & Units when the estimate at completion must not change, and
- Fixed Duration & Units/Time when the crew size must remain constant.
The table on the right displays what happens to the relationship in each of the four options when one variable is changed and
- The User Preferences, Calculations tab option Preserve the Units, Duration, and Units/Time for existing assignments is selected.
The table on the right displays what happens to the relationship in each of the four options when one variable is changed and
- The User Preferences, Calculations tab option Recalculate the Units, Duration, and Units/Time for existing assignments based on the activity Duration Type is selected.
- Bold descriptions in the right column in the table indicate the differences from the upper table.
- The User Preferences, Calculations tab option Preserve the Units, Duration, and Units/Time for existing assignments will not freeze the Activity Units when the Duration Type of Fixed Units is selected.
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