Primavera P6 Calendars, Activity Durations and Hours per Time Period Explained
Written on . By Tracy Mah
After creating a calendar in Primavera P6, additional steps need to be taken to ensure the durations entered for the activities are correct. Project managers and schedulers may have encountered discrepancies with the length of their tasks, the calculated expected finish date and the budgeted resource hours for each activity.
When creating a calendar, most Primavera P6 Users are familiar with setting the calendar’s workweek hours. There is an additional step to consider, which is a conversion factor between the displayed duration of the activity to how it is stored and used for calculations in the P6 database.
Changing the Displayed Original Duration Format of Activities
Steps to configure the Duration Format in P6 User Preferences:
- On the Menu Bar, click Edit.
- Select User Preferences.
- Click the Time Units tab.
- In the Durations Format field. Select the desired Unit of Time from the dropdown menu.
- Optional: Checkmark the Show Duration Label. This will display h (hours), d (days), w (weeks), or y (years) label for any duration column.
Figure 1 and Figure 2 shows the Original Duration displayed in Days and Weeks.
Regardless of which format you choose to enter for your activity durations, the length of each activity must be stored in the Primavera P6 database. Hours is the base unit Primavera does its calculations. P6 uses a conversion factor to change whatever duration that is displayed for the activities to be changed to hours.
Unit Conversion Analogy
As an analogy, let’s look at the simple formula of Velocity = Distance divided by Time (V=D/T). If you wanted to measure velocity in Kilometers/Hour but were given distances in meters or miles and time in minutes or seconds. The calculation for velocity cannot be done with the different units. Everything would need to be converted to the same units of Kilometers and hours for the equation’s calculation.
The same concept applies in Primavera. The conversion factor is controlled in the Calendar assigned to the activities called Time Periods.
Setting the Calendar Workweek and Hours per Time Period
When creating a calendar in the Calendar dialog box, the Workweek button is used to define how many standard work hours there are for each calendar day, Monday thru Sunday. Even though the hours per day are defined here, P6 does not use these values to convert the activity’s Original or Planned Durations displayed on the Activity Table to hours. The Time Periods button is used to ‘Specify the number of work hours for each time period’. You must manually enter how many hours there are for each Hours/Day, Hours/Week, Hours/Month and Hours/Year Time Period.
In general, it is only necessary to have the Hours/Day to be accurate to match the number of hours defined in the Workweek. For the most part, project managers usually prefer to enter their activity durations in days. It would be very rare to enter a duration in weeks, months or years for the length of an activity. Therefore, it isn’t vital to ensure the hours per week, month or year are accurate unless you do enter your activity durations in weeks, months or years. The example in Figure 4 is a 10 hour x 5 day Calendar with the correct Workweek Hours and Time Period Hours/Day.
What if the Project Activity Durations are in Hours?
If you manage your project in Hours or enter your activity durations in Hours, like most Shutdown, Turnaround, and Outage maintenance projects. Then you don’t have to worry about the Time Periods because there is no need to convert the displayed activity duration of hours on the activity table to be stored as hours on the database.
What happens if the Workweek hours/day and the Time Periods hours/day don’t Match?
As an example, let’s say you created a project calendar of 10 hours per day for 5 days a week. But forgot to adjust the Time Periods and left it to the default 8 hours per day (Figure 5). If you had an activity that was 1 day in duration, you are expecting it to be one 10 hour day. However, the Time Periods conversion for that calendar is 8 hours, therefore, Primavera will be treating that task to be 8 hours in duration for each day instead of 10 hours.
Time Period Effect on Resources
Additional consequences of this mismatch extends to resource assignments. When assigning resources to an activity, the resources are assigned using the hours converted from the Time Period not the calendar Workweek hours.
If we use the 10 hour/5 day Calendar from Figure 5 with the incorrect Time Period of 8 Hours/Day and assigned a Resource to a 1 day activity. Based on the Time Period Hours/Day, P6 will convert the 1 day duration activity to be stored as 8 hours in the database. As a result, the Resource is assigned 8 hours Budgeted Units, not the 10 hours as we expect as shown in Figure 6.
If we use the 10 hour/5 day Calendar from Figure 4 with the correct Time Period of 10 Hours/Day and assign a Resource to a 1 day activity. We expect the Resource to be assigned Budgeted Units of 10 hours because P6 correctly converted the 1 day duration activity to be 10 hours long. As we can see from Figure 7, the Labourer Resource has the correct 10 hour Budgeted Units.
Calendars in Primavera P6 may bring some confusion to Project Managers. They may find discrepancies between the Activity Durations, Resource assigned hours and Calendars. It is an important step when defining the Calendars for your project to double-check that the Workweek’s Standard work hours matches the Time Period Hours/Day. This ensures each Activity’s Durations are correctly converted to hours for the P6 database.
Why are Time Periods Used?
The Time Period ‘conversion factor’ that is defined for each Calendar allows the flexibility to use more than one calendar in the project. By bringing all of the displayed activity durations to the base unit of hours this gives the ability to assign different calendars to tasks throughout the project. For example, work tasks for office personnel are scheduled on an 8 hour day, while activities for trades working on site are scheduled on a longer 10 hour day.
Being aware of how the displayed activity Durations, Calendar Workweek and the Calendar Time Periods are all tied together helps to resolve discrepancies in the project schedule.
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