Primavera P6 has quite a few date fields that are often misunderstood. Perhaps no date field is stranger than the “planned” date. To begin with, there will always be a Planned Start and a Planned Finish date associated with every activity. In a schedule with no progress (or what we would traditionally call the “baseline” if P6 did not use this designation for target schedules) the following is always true:
- Planned Start = Start
- Planned Finish = Finish
Once progress is recorded, however, all bets are off. The planned dates will not reflect actual dates, for example. Primavera P6 shows actual dates in the Start and Finish columns, making it easy to see which activities have progress (take that, Microsoft Project!) without having to add the Actual Start and Actual Finish columns. Space is always at a premium in a printout so not having to add the actual columns is a nice benefit.
Here is where it gets interesting. Changing the Planned Start or Planned Finish date on an activity with no progress will change the Start and Finish dates and likewise move the bar in the Gantt Chart. The rules are:
- Changing the Planned Start changes the Start date, even if the Planned Start is before the original Start date
- Changing the Planned Finish moves the Finish date and changes the Original Duration to match
- Changing the Planned Start and Planned Finish will move the Start and Finish dates accordingly
- No other activities are affected by changes to the Planned dates of an activity
None of this will happen, however, if the “Schedule automatically when a change affects date” scheduling option is selected. This is because scheduling the project wipes out the changes made to the Planned dates. These are not constraints, after all. The logic was never modified. Which may seem like Planned dates are a cruel trick.
Well, we create logic for a reason. Moving bars around is not scheduling. Logic is supposed to drive dates. A few constraints are okay – although some owners are adamant about having none – as long as they do not cause an interruption to the critical path. Postponing the start of a critical activity would obviously make no sense.
Note that if you change the Planned Start or Planned Finish of an activity with progress, nothing happens at all. The Planned dates will not change.
Changing the Planned dates, really, is mostly a bad idea. But let’s say we all agree that some of the dates in a schedule are not right. So we massage the dates using the Planned columns and then create a baseline. Using the baseline as a guide, we then modify the logic and durations to achieve the new dates. Sort of like tracing a drawing with velum paper.
Comments or questions? Please feel free to contact me.