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All posts tagged P6 Calendars

The Makings of a Complicated Schedule

Categories: Activity Types, P6 Calendars, P6 EPPM, P6 Professional
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Primavera SchedulingWhen does a Primavera P6 schedule become complicated? I realize that for new users it might seem like every schedule is hard; but their problem is a lack of training or experience, not the schedule itself. Schedules with thousands of activities take more time to assemble, but that alone does not make them more complicated. Besides, in nearly every schedule there is repetitive work, so we can often copy dozens (if not hundreds) of activities quickly and reuse them. If you do not already know how to do this, read Time-Saving Tricks in P6 You Must Use.

Having prepared hundreds of original plans and thousands of updates, I can say for certain that two characteristics in particular complicate a Primavera P6 schedule. There are other situations that make a scheduler’s life “interesting” but trust me, these two are the biggies:

  1. The schedule has more than one calendar
  2. The schedule is resource loaded

Having more than one calendar is, mind you, often a necessity. The project specifications may require that inclement weather days be added to the calendar. In other words, anticipated weather days must be blocked out similar to holidays and other non-work days. But not all activities will be affected by weather (shop drawings, permits, interior finishes, etc.) so we must also utilize a calendar that does not have weather days.

Another reason for more than one calendar would be that some activities can occur any day of the week without exception, such as concrete curing, or the project specifications identify certain tasks accordingly. So now we have a 7- day calendar in addition to a work calendar with weather, and a work calendar without weather. Just like that the schedule has three calendars!

Okay, but why is it such a big deal to have multiple calendars? To start with, strange things can happen as the schedule moves from one calendar to another. Here is one possible scenario:

The predecessor finishes on Saturday because it obeys the 7-day calendar. If the successor has a 5-day calendar, it cannot start until the following Monday. Even though both activities might be on the critical path, the predecessor will have one (1) day of Total Float while the successor has zero (0) Total Float. After all, the predecessor could have finished on Sunday and still not hold up the successor.

In Primavera P6, Total Float is relative to the activity calendar so two activities on the same path may not exhibit the same float value if they have different calendars. By the same token, activities with the same Total Float value may not be on the same path.

Here is another possible scenario: the predecessor has a calendar that is 7:00 am to 4:00 pm. The successor has an 8:00 am to 5:00 pm calendar. The relationship between them is Finish-to-Start. The successor will start the same day the predecessor finishes because there is still one hour left in the day (i.e. 4:00 to 5:00 pm). This can confuse a lot of people who never display the time of day on their schedules. They think the activities are overlapping somehow when in reality they are not.

Moving on the resources, there is a calendar issue here to consider as well. Resources cannot use project calendars. Only global and resource calendars can be assigned to resources. Our students know why we prefer to use project calendars on every project. But the moment resources are added we are stuck with global or resource calendars. There is some logic here on Oracle’s part. Resources are not project-specific and so only a shared type of calendar would be appropriate.

So think about it. We already had three calendars because of weather and the need for a 7-day calendar and now we have a fourth one! The schedule can get seriously weird at this point. What if the resource plays by different rules than any other calendar? Well, our strategy is to create a global calendar first, copy it as a project calendar, and also assign it to the resource. So the project calendar and the resource calendar are identical.

There are situations where the resource works different hours or different days and should take over in terms of calculating dates. Perhaps the resource is never available on Fridays. We have to consider whether the project or resource calendar is more important. This is why Primavera P6 offers Task Dependent and Resource Dependent activity types. There is no single right answer; it depends on the circumstances.

The question in my mind when it comes to resources is, “does the dog wag the tail or does the tail wag the dog?” If the dog is in charge then I want a Task Dependent activity. Then it won’t matter if the resource calendar does not align with the activity calendar.

Another consideration with resources is that we can allow Primavera P6 to change the activity duration – something that would never happen otherwise. Therefore, the Duration Type becomes a very big deal. Should we let this happen? It does introduce additional moving parts to a schedule that might be difficult to understand due to other reasons such as multiple calendars. Still, it does make sense that if I know the budgeted hours and the crew size, why not let Primvera P6 do the math?

And of course, if we resource-load a Primavera P6 schedule we can also resource level the schedule. I teach this in my intermediate and advanced classes, albeit with the caveat that it takes several iterations of resource leveling before we can be satisfied that the optimum answer has been found: finishing as quickly as possible using a reasonable number of resources. Not exactly something the Pharaohs worried about but for us mere mortals, time and resources are limited.

Sometimes, giving priority to the earliest activity that needs the resource yields the best result. Other times it is better to give priority to the activity with the least amount of float. If I want a very precise allocation of resources I will utilize the Activity Leveling Priority. Unless you know what all of this means then it would be unwise to resource level a schedule without guidance.

Owners may not like the idea of resource leveling because it reduces the Total Float that contractually is almost always shared between owners and contractors. But sequestering Total Float is not the idea. One of the best schedules I ever saw (that wasn’t mine) was a resource-leveled schedule on a project in Hong Kong. The owner thought it was madness but it definitely worked.

I have not touched upon everything to consider with multiple calendars and resources, but hopefully the point has been made. Complicated schedules are frequently unavoidable, often necessary, and must always be respected. Are you ready for the challenge?

Claim Digger Limitations

Categories: Claim Digger, P6 Calendars, P6 EPPM, P6 Professional, P6 Tricks
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Primavera SchedulingClaim Digger is a convenient tool inside Primavera P6 for comparing schedule files to determine what changes have been made. But there are limitations to what Claim Digger can tell us about a revised file. Experienced Primavera users will recall that Claim Digger used to be a third-party program used to analyze Primavera P3 files. When Claim Digger was incorporated into Primavera P6 several years ago the functionality changed in ways that were both good and bad. Being able to export to HTML format is nice, but having the durations (including float and lags) displayed in hours is inconvenient on schedules with durations that are shown in days.

There are third-party software programs that can do much more than Claim Digger. Still, if you think that Primavera P6 costs as much as having a baby then anything that is “free” will be the most desirable option. So most of us will have to get by with Claim Digger until money starts growing on trees.

Note: in Version 16.1 of Primavera P6 Claim Digger is now called Schedule Comparison and is accessed from the Visualizer program. You will find Scheduler Comparison in the same location (Tools) as Claim Digger but clicking on this button will launch the Visualizer program.

The biggest limitation in Claim Digger has to do with calendars. Here are two scenarios where Claim Diggers will let you down:

  1. Changes made to a calendar, such as revisions to the number of hours per day, days per week, holidays, etc. are not picked up by Claim Digger
  2. Changing the calendar on an activity from Global to Project (or vice versa) is not picked up if both calendars have the same exact name

Indeed, Claim Digger will tell us nothing about calendars other than whether the name of the calendar is different. To demonstrate this for myself I created a Project calendar called “Standard” that is a copy of a Global calendar with the same name. I assigned the Global calendar to all of the activities in a sample project. After creating a baseline (copy) of this project I switched the calendar on the activities in the current project to the Project calendar. Claim Digger did not report any changes to calendars.

I then changed the name of my Project calendar in the current project to “Standard Days” and re-ran Claim Digger. As I expected, Claim Digger reported that I had changed the calendar. Yet other than the name, it was still the same Project calendar. I hadn’t changed anything else. In other words, a false positive.

Owners often run Claim Digger (or ask for the results) so anything that suggests a change when in fact no change was made creates unnecessary confusion. Conversely, a sneaky scheduler could block out additional days in the calendar to coincide with an owner-caused delay in order to exaggerate the impact. An experienced scheduler should be able to figure out if there are any shenanigans going on, but the reality is that P6 is chock-full of hidden traps for the uninitiated.

While we are on the subject, I often refer to myself as a “Primavera P6 Scheduler” because there are in fact specific techniques to scheduling projects with Primavera P6. Case in point: Microsoft Project does not allow two relationships between the same two activities, while in Primavera P6 this is perfectly acceptable. A good scheduler with poor Primavera P6 skills can still make a lot of mistakes because of their unfamiliarity with the program. For the same reason, I tend to be very cautious in Microsoft Project because it is not my bread and butter.

I started using Primavera software in 1987 so in my mind the rules that I observe have almost always been specific to one particular program. Prior to 1987 the software I used was proprietary and followed basic Critical Path Method rules. But CPM does not teach you about Activity Codes, Resource Leveling, and so many other things that are now possible because of software any more than an accountant would automatically know how to create a macro in Microsoft Excel.

“Old-school” schedulers who refuse to stay current on scheduling software get no sympathy from me. I started with proprietary scheduling software, learned Primavera P3, followed by Primavera SureTrak, Primavera Primavera P6, Primavera Contractor, and Primavera P6 EPPM. Not to mention all of the other programs like Microsoft Office that I have had to learn over the years. I had to learn WordPress just to type this silly blog!


The Pitfalls of Using Multiple Calendars

Categories: P6 Calendars, P6 Optional Client, P6 Professional, P6 Web
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Projects often require more than one calendar. For example, the office personnel work 8 hours per day, but the field personnel work 10 hours per day (a good reason to be stuck indoors, I suppose). Another reason might be that some activities involve a process that continues around the clock – concrete curing or a test that has to be performed continuously for several days. One of my clients manufacturers most of its components overseas and uses a 7-day calendar for shipping the components to the United States but the fabrication activities are based on a 5-day work week with holidays. So multiple calendars is a sensible approach.

Nevertheless, using more than one calendar on a project is liable to create issues in Primavera P6. Activities will seemingly start or finish on the wrong day. In most situations we would expect that with a Finish to Start relationship the predecessor finishes the day before the successor starts. This is unlikely, however, if the number of hours being worked each day do not match for the predecessor and successor. In the following example I have a predecessor using an 8-hour calendar and a successor using a 10-hour calendar:

Multiple Calendars_Before


The 8-hour task has a start time of 8:00 am and a finish time of 5:00 pm with a 1-hour lunch break. The 10-hour calendar has the same start time but the workday does not end until 7:00 pm. Therefore, the successor can work for two hours on the same day that the predecessor finishes. Since most users do not show the time of day in the date columns it will appear that the relationship between these two activities is something other than Finish to Start.

This problem will reverberate throughout the schedule as one activity after another starts and finishes slightly off the usual time. In order to locate the source of the problem I will sort the activities by the Start date, display the time of day in the date columns and look for the first task that does not start at the usual time.

But how do we stop this from happening in the first place?

The solution is quite simple. Give the 8-hour calendar and the 10-hour calendar the same start and finish times.

I know what you are thinking. The math doesn’t work!

Well, it just takes a bit of fibbing. See, I create an 8-hour calendar with a 2-hour lunch break and a 10-hour calendar with no lunch break. Now both calendars have the same start and finish times. Problem solved. (Our company slogan is “Problems Solved” but I will settle for just one right now).

My solution is displayed below:

Multiple Calendars_After


The reality is that most users do not want to see the time of day in the date columns so the 2-hour lunch break has no effect whatsoever. I seriously doubt some worker will disappear for two hours because of the CPM schedule. If he or she does, I will buy them lunch!

Some of you might wonder why we should have two different calendars at all if the start and finish times are going to be exactly the same. Well, for resource-loaded schedules it is important to have the hours per day match expectations.

My oil & gas and nuclear clients who schedule by the hour would never submit to this ruse because the time of day will of course be displayed. It is not enough to say an activity starts on, say, Monday, because the activity durations are just a few hours typically. So the next task starts the same day. But for the rest of us this solution works quite well.

I employ a similar strategy for my 7-day calendars. I make sure that the start and finish times match my other calendars. Which means my concrete curing activities typically start at 8:00 am, take a lunch break, and stop at 5:00 pm if my other calendar is an 8-hour calendar. Using a 24-hour calendar would just make things too complicated.

Any questions? Fee free to contact me.