Identify and Understand the Reasons for P6 Rounding Errors
Many companies like to keep their schedules on a daily basis so that all activities start at the start of the day, finish at the end of the day and all durations are in round days. P6 does not have functions like the Elecosoft (Asta) Powerproject “Snapping” function that keeps all task to a round day, so users have to be more careful with Primavera P6.
There are two issues in P6 with rounding errors:
- Firstly, how do you identify that you have rounding errors and
- Secondly, identifying what is causing rounding errors.
The picture on the right shows:
- A1010 is a one-day activity but spans two days and
- A1020 should finish on Friday but goes over the weekend.
This paper will look at both issues.
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User Preferences
In P6 User Preferences are user centric. It would be better if many of the User Preferences were Project Preferences.
Also, the formatting set in the User Preferences apply to all views and for all projects in P6 and the user must continually change them, depending on what the user is doing. It would be better if the user could format dates and times for each Activity Layout, but this is not possible.
As a result, a user must be careful how they set their User Preferences and must continually change them depending on what they are doing.
Time Unit Formatting
It is recommended that users always display the Sub-unit in the Duration column to allow them to see if there are any non-round or whole days.
To adjust how the date and time are displayed:
- Select Edit, User Preferences…;
- Select the Time Units tab;
- The Duration Format section determines how the activity durations are displayed and should be set as per the picture on the right;
- The Duration format above is recommended by the author so any non round durations will be observed.
Date Formatting
Date Format:
It is recommended that users always display the Month name on all international projects so there is no confusion between the US mm/dd/yy format and the ROW (Rest of World) format of dd/mm/yy.
Time Units:
It is STRONGLY recommended that the time is ALWAYS displayed in 24-hour format so the user knows the time of any selected date. This is because the software will often select 00:00 (the first minute of a day) when assigning dates. The author does not display minutes to keep the date column widths slightly narrower.
To format these settings:
- Select Edit, User Preferences…;
- Select the Dates tab;
- The settings on the right are the recommended settings when creating a schedule, but the time should be hidden when printing reports.
Once the User Preferences are set then the cause of rounding errors are clear, Activity A1010 has a 1-day and 1-hour duration that is pushing the other activities out.
Causes of Rounding Errors
You may find that your activities are not starting at the start of the day or ending at the end of a day, or a one-day activity is spanning two days etc.
Firstly, it is important to understand that P6 rounds down values of *.5, so 8.5 is rounded to 8 and 8.51 is rounded to 9.
The possible reasons for rounding errors or display issues are:
- The activity Duration is not a round figure and the display has been rounded down, but you are not showing decimal days or days and hours settings in the User Preferences.
- The Remaining Duration is not a round figure and the display has been rounded down. This is caused by using Duration % Complete.
- The calendars do not have the same number of hours per day for every day in a calendar.
- The calendar Hours per Time Period do not match the calendar hours per day.
- The activity is not starting at the start of the day. Check if there is a change of calendar from one activity to another. One way to stop this happening is to have all calendars in a multiple calendar schedule ending at the same time.
- The Project Start Date is not aligned with the calendars. For example, the project start is at 08:00hrs but the first activity calendar is set to start at 07:00hrs.
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