All posts tagged Level of Effort

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Apr

My Least Favorite Activity Type

Categories: Activity Types, Level of Effort, P6 EPPM, P6 Professional, WBS Summary

Tags: Activity Types, Level of Effort, Primavera P6, WBS Summary

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by Bill Pepoon

While I consider my self pretty adventurous when it comes to Primavera P6, I admittedly have little use for one particular activity type, the WBS Summary. To review, the WBS Summary calculates its Start and Finish date (and therefore, duration) from all other activities that have the same WBS code. On the surface, this seems like a great idea because logic is not required. The WBS Summary is the only activity type in Primavera P6 that works sans logic. And this is what I do not like about it.

I always check the Schedule Log before I publish a schedule. As you should know, the Schedule Log has a topic called “Warnings” that discusses, among other concerns, the number of activities that are missing predecessors or successors. The correct number of “open ends” would of course be two; the first activity will not have a predecessor and the last one will not have a successor. No other answer is acceptable. Owners will also be checking the Schedule Logs during their reviews. Open ends are an easy way to get a schedule rejected.

Because the WBS Summary does not want or need logic, it creates what appears to be a de facto mistake in the schedule. If the person reviewing the schedule figures out that the open ends are due to this particular activity type, then perhaps they would accept the schedule regardless. But it has been my experience that owners do not want to hear any excuses as to why some activities have logic and others do not. Open ends are an unnecessary distraction from other items (sequences, durations, coding, etc.) that need to be checked.

It is possible to add relationships to a WBS Summary to make the open ends disappear, but this basically defeats the purpose of having them in the schedule in the first place. Why not use the Level of Effort instead? The Level of Effort also calculates its dates and duration automatically, but requires logic. Therefore, the Level of Effort does not create any concerns in the Schedule Log. Both of these activity types can also have resources assigned, so nothing is lost by switching to the Level of Effort.

Logic can be added to a WBS Summary without affecting the way it calculates its dates and duration, but again, why not use the Level of Effort instead? While they may seem interchangeable, the Level of Effort demands logic, and therefore forces us to add proper relationships. The WBS Summary is a little too accommodating. I want my activity types to enforce good habits!

Better still, the Level of Effort can transcend more than one WBS code which makes it far more flexible than the WBS summary. If I really need to see the dates and durations for WBS codes I can Group by WBS and choose to Show Group Totals. This saves me the trouble of adding a bunch of WBS Summary activities to my schedule for no other purpose than seeing summary dates and durations.

In the screenshot below, the WBS Summary activity is purple. Yes, this activity tells me the Foundations start on May 17 and finish on June 28, 2016 and have an overall duration of 30 days. Yet the same information appears in the Group Totals:

So there is no additional benefit to adding the WBS Summary activity if the only information being provided are the summary dates and duration.

I know some users are adding WBS Summary activities as a simplified way of cost loading a schedule from the top down. They put all of the costs in the WBS Summary activities rather than the actual work tasks. But Primavera P6 has a tool called Top Down Estimation that is better suited for that purpose. While it is possible to specify a non-linear distribution curve for resources, the reality is that you are still treating every day as having the same value. That is simply unrealistic.

A Primavera P6 compatriot did mention to me a reason why he uses the WBS Summary activity on a temporary basis. When Microsoft Project schedules are imported into Primavera P6, the summary bars are imported as activities. He uses the Microsoft Project summaries as temporary placeholders for checking logic and durations. Similarly, I will use the descriptions of the Microsoft Project summary activities to build my WBS codes before deleting these superfluous tasks,

Dec

Weird Negative Float Situations – Part 1

Categories: Level of Effort, Primavera P6, Schedule Options

Tags: Level of Effort, negative float, Primavera P6, schedule options

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by Bill Pepoon

Most of us understand that negative float is generated by a constraint that is not being “satisfied” and indeed, we cannot have negative float without a constraint. Or so it would seem. But during a recent training session at the Kennedy Space Center my client showed me several Level of Effort activities that had negative float. In fact, all of the Level of Efforts had negative float yet no other activity showed any negative float whatsoever. Imagine that; the activities linked to the Level of Efforts have positive float but the Level of Efforts have negative float!

In the first figure I am showing a typical setup with a Level of Effort activity linked to one predecessor and one successor. The Activity Type is shown in the Activity Table to make it easier to see which activity is the Level of Effort:

Okay, so far nothing is amiss. The Level of Effort is linked to activities on the critical path and therefore shares the same zero (0) float. But watch what happens when the predecessor to the Level of Effort is updated with progress:

The Level of Effort activity – and only the Level of Effort – has negative float! Keep in mind that no constraints are being used in this schedule. And while all of the Task Dependent activities are on the critical path I can assure you this has nothing to do with the negative float on the Level of Effort activity.

So how is this possible?

The answer has to do with the ability in Primavera P6 to calculate float three (3) different ways. These settings appear under Schedule Options:

I typically calculate float as the difference between the Late Finish and the Early Finish dates. But my client had selected Late Start – Early Start. (The third option is to take the smallest value of the two calculations). Choosing any setting other than Late Finish – Early Finish will generate negative float once the predecessor to the Level of Effort has started. Moreover, astute viewers will notice that the negative float matches the number of days that have elapsed since the predecessor started. The predecessor started five work days before the Data Date and the float is -5 work days.

Why this is happening is a little hard to explain, but Primavera P6 calculates float for both the start and finish of every task. Normally this results in the same value. Level of Effort activities, however, are another matter. Primavera P6 calculates the float on this type of activity as the difference between the Actual Start Date and the Data Date and perceives the activity as being “late” because the Data Date is later than the Actual Start Date.

Thankfully this weird float issue can be easily avoided by using Late Finish – Early Finish for the float calculations. And while this has always been my personal preference I have a whole new appreciation of this setting now.

Apr

Every Schedule Needs a “Hammock”

Categories: Primavera P6

Tags: Hammock, Level of Effort, Primavera P6

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by Bill Pepoon

Granted, we do not call them Hammocks any longer because P6 introduced a new label: Level of Effort. This is of course an activity type. Why Oracle decided Level of Effort is a better description is rather baffling. During our training classes when we talk about Hammocks most people get the analogy of something that spans from one place to another, just like the hammocks you might see in a backyard. Simply put, a Level of Effort activity measures the distance between a predecessor and a successor. Why is that important?

We typically use a Level of Effort activity to measure the project duration. This is the only accurate means of measuring the project duration if more than one calendar is being used. We assign the Level of Effort activity a calendar that matches the calendar used to specify the project duration. So if the project is supposed to finish within 300 calendar days, we give the Level of Effort activity a 7-day calendar with no holidays.

Another excellent use of this type of Level of Effort activity is to represent overhead and profit on a cost-loaded schedule. Since the Level of Effort activity already mimics the project duration, it gives us a per diem distribution of overhead and profit for the life of the project. This is much easier than trying to add overhead and profit to each activity in the schedule.

In the example below, Activity ID 01 is a Level of Effort activity with two predecessors, and two successors. When there is more than one predecessor, the earliest Start date becomes the Start date of the Level of Effort activity and the latest Finish date becomes the Finish date of the Level of Effort activity. For this to work right, the predecessor relationships must be Start to Start and the successor relationships must be Finish to Finish.

Any activities can be linked with a Level of Effort activity, so this is not always about “effort”. We could link the Start date of the first piping task to the Finish date of the last piping task and this would give us the overall duration of piping work. But if we tie the Level of Effort activity to something other than the first and last piping tasks we are not describing the overall timeframe for piping correctly. A WBS Summary activity is another option (which we will discuss later) if the only goal is to show a summary bar. Keep in mind, the duration of a WBS Summary activity may be incorrect unless all the activities it summarizes share the same calendar.