When it comes to CPM scheduling in the construction industry, generally, the smallest unit of time is measured in Days. In fact, many construction specifications state this categorically. However, in P6, the Duration, Total Float, Free Float, Lag values, or date that is displayed on the screen may be different from what is actually stored in the P6 database.
For example, if an Original Duration of 40 Days is assigned to an activity with a 5-Day calendar set to 8 Hours per Day, the value stored in the OD field (named Target_drtn_hr_cnt) is 320.00. In other words, P6 stores duration values in hours. (See Activity E in the illustration below).
In the illustration below, Activity ID A1020 and A1060 both have an Original Duration of 25 Days. However:
- A1020 was updated by assigning a Duration Percent Complete of 35%.
- A1060 was updated by assigning a Remaining Duration of 16 days.
P6 calculates the Remaining Duration for A1020 as 25*(1-.35) or 16.25 Days. The .25 remainder (or 2 hours) is reflected in the finish date as 09-Jun-16 10:00 (10AM). Meanwhile, A1060 displays the same Remaining Duration as A1020; however the finish date is reflected as 08-Jun-16 at 17:00 (5PM). Furthermore, A1060 is not on the Critical Path even though the Total Float value is displayed as 0 (the Duration Format Decimal value for the Day Unit of Time is set to 0).
The Partial Day effect can even cascade throughout the CPM Network affecting Total Float and Free Float values.
- Analysis Report #26 illustrated below displays activities with Partial Original Duration, Remaining Duration, Total Float or Free Float values. Notice that although A1040 and A1060 have non-Partial Original Duration and Remaining Duration values, their Total Float and Free Float values are indirectly affected by the Partial RD of A1020.
2. Analysis Report “Partial Original or Remaining Duration” is a subset of Report #26 with the same format and display parameters.
3. Analysis Report “In-Progress Tasks with Partial Remaining Duration” is also a subset or Report #26 with the same format and display parameters.
4. In the illustration below, Analysis Report #27 identifies activities with Partial Lags.
In all the Zümmer Analysis Reports referenced above, the duration values are formatted in Days to rounded the nearest tenth. This format can also be replicated in P6 by changing the User Preferences in the Time Units tab Duration Format Decimals settings to 1 as shown below.
In addition, in P6, the dates can be set to show time values by changing the User Preferences Dates Tab Time section to 24 hour or 12 hour as shown below.
After printing or previewing the Zümmer analysis reports, find the partial day activities and/or relationships and revise the duration values accordingly to the nearest whole day. Since Total Float values are cascading, it is suggested to start with activities sorted by Early Start.
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