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Remaining Durations - Adjusting

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Sally Ryan
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Hello All,  I have a query which has been bothering me:

I'm not sure what the correct way to deal with remaining durations is. I use Primarvera P6.


Activity  - Excavating Trench. Original Duration of 10 days.


Activity Starts 1-Nov.  You update progress onto this activity and reschedule your programme at the end of the week with data date 8-Nov.  7 days have gone past.  Your original activity duration was 10 days.  If you have completed 25% of your work - does that mean you have theoretically used 2.5 days worth of your original duration - thus adjusting your remaining duration to 7.5 days?  Just because you have started this activity and worked on it - doesn't mean that you have used the entire 7 days during the week - you may have only used half a day. But it's impossible to know this with hundred of activities. 

What do others do in this situation?  When / how / why should you adjust an activity's duration?

Obviously on a large programme you can not ask PM remaining durations on each and every activity at the end of each reschedule.


Also - does anyone run a programme whereby you set all activities with an expected finish (as per baseline dates) at the beginning of the job and then each time you reschedule - the activity duration adjusts itself (shortens) to keep in line with expected finish.  Then continue doing this until your manning increases too high in a specific area and then highlight this to PM who will then decide what he wants to do - ie increase manning to that level OR push out completion date?

This has been suggested to me as an appropriate way of scheduling.

Any feedback would be appreciated.


Rafael Davila
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Joined: 1 Mar 2004
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From the figure above assume all activities are similar, 10 day planned but for illustration purposes progressed differently.

You can update an activity in several ways:

  1. You can assume progress as planned and let the software do the math, but this rarely happens. Maybe if this is how you plan to update your activities you can tell the PM you already finished the baseline and science everything will happen as planned he should send your check to your home as you will be taking a sabbatical. See activity 1
  2. You can report for the update period a total value of actual work hours [not necessarily equal to planned for elapsed period] covering the whole or a single portion of the update period and let the software evenly distribute the hours. See activity 2. This seems to me the minimum you shall do.
  3. You can report for the update period individual progress on a day by day basis. See activity 3. This gives you all detail but time consuming. Usually I would opt for option 2 and leave this option 3 only for activities under owner disruption and with risk of becoming part of a delay/disruption claim. Here equally important would be to record the production on every individual period.

I used Spider Project to illustrate the issue, if you use other software the concepts are the same; you record true actual data and estimate planned remaining duration based on your true plans for after new DD. Spider Project users make use of volume of work to define productivity as an hour of effort for different resources does not yield same production. Percentages tell us even less when comparing work and disruption among different activities; for example 100% of activity A can mean 10,000 masonry units while 100% of activity B can mean 28,000 masonry units. With percentages it is difficult if not impossible to make use of the "measured mile" approach in a direct and transparent way. We speak the language of the construction contractor.

Hope my comments can be of some help.

Best regards,


Gary Whitehead
User offline. Last seen 2 years 33 weeks ago. Offline


It's all too common to have a PM who isn't interested in good practise scheduling. Often it is because the schedule is only really there to report on historical progress, rather than as a project management tool to control the remaining works. If however your PM does genuinely expect the plan's forecast dates to be accurate, then keep badgering away with plenty of "I told you so"s each time the automatically-calculated remaining durations prove to be wrong (and they will. Frequently).

It's pretty much impossible to force good planning practise on a PM, without the buy-in of senior management. All you can do is keep plugging away.


As for the trench scenario -you wouldn't need to be capturing all the permuations you mention on a day to day basis -the foreman or supervisor can manage that. What you need to do is for each (weekly or fortnightly or whatever) status update, talk to the foreman about any progress that varied from the plan (either ahead or behind), find out the reasons why and make sure any reasons that are still ongoing are factored into the remaining duration esitmate, and any reasons that are no longer ongoing are not factored into the remainnig duration estimate. -Essesntially you want to ensure that these estimates are based on intelligence rather than a simple formula.


Just to be clear, if you are planning for an electrical subby, I wouldn't be tracking the civil or Mech install work in this manner. -I would just have the relevant access dates as milestones in your programme, and get them to update you with any changes to these milestones. -Let them plan & monitor their own work.


Your final question ref cable runs: -it is often a challenge to work out what the best level of detail to plan down to is. Normally, I try and limit my activities to no more than 1 week, but it very much depends on the type of work you are doing -If your planning a shutdown & maintenance of an offshore oil-rig for example, you might find yourself planning down to the nearest minute.

As a general rule, I would split your cable runs into chunks of work as big as possible, but which satisfy the following conditions:

1) No more than a week long

2) Same resource(s) used

3) Same predecessors and successors (eg access milestones, sub-system commissioning, sectional completions, etc)

4) Same activity (ie laying cable should be seperate from terminating)

Once you've done this, it's rare that you will find activities that are "stopping and starting", and it should be quite easy to measure Physical progress -metres of cables laid or No. of terminations made, etc.


Don't be afriad of having hundreds of activities in your programme, if that's what you need to make it accurate and reliable. -Also bear in mind that the workload to update does not increase linearly with the number of activities. For example, if you are updating every week, and for now assuming none of the activities take longer than expected:

Option 1: A single 4-week activity will be in progress and hence need to be updated 4 or 5 weeks in a row

Option 2: 4 x 1 week activiities will need to be updated 1 or 2 weeks in a row each, meaning 4 to 8 activity updates in total.

So a 400% increase in the level of detail of your programme will generally only mean a 50% increase in the workload to keep it updated

(There is of course also the additional one-off work to create the more detailed schedule to consider)






Sally Ryan
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Thanks Gary,

I was quite suss on the 'expected finish' dates myself. It seems a lazy way of doing things but I can understand how it could also be useful in some instances.   Another planner suggested this method of rescheduling to my PM and he seems to think it's the way we should run the programme. PM seems to think remaining durations should be and 'are' calculated automatically by P6 and he gets frustrated every time that I ask him the remaining durations for activities.


As for the trench scenario:

Perhaps the work on the trench was only able to be done sporadically, a bit here, and a bit the next day. Stop for one day completely and then start again the next day.  Next thing a week has gone by and you have done only a few days work out of the whole week. Perhaps it was a 6 man job for the week and then out in the field they decided to only put 2 guys one day and 2 another day due to manning required in areas elsewhere.   It seems to me almost impossible to capture all of this on a day to day basis.  I am working for an electrical contractor - where unforunately our role is to get in where we can / when we can - dependant on access / completion of the civil contractor - just so we can get the job done - this almost always is not according to our baseline dates.  I rarely go out on site as PM feels not necessary and to just gather the information directly from supervision at the end of the week.

Another issue is having an activity that was Installing Cable in one area. The hours in this activity will cover perhaps 30 different cables.  Obviously all 30 cables cannot be scheduled to begin installation on the same day and it would not be feasible to break down your schedule to create an activity for each separate cable installation / termination etc - this could be hundreds of separate activities. It's just not a realistic option.

It's really quite difficult to capture the stopping and starting of each activity if the activity includes more than one action (if that makes any sense).

Does anyone else have this problem or a problem similar?


Gary Whitehead
User offline. Last seen 2 years 33 weeks ago. Offline



1) Excavating trenches is one of the more linear types of work out there. -That is to say if you have 75% of the trench left to excavate, it MIGHT be reasonable to assume it will take approx 75% of the original duration or 7.5d.

But first you need to understand why the first 25% took longer than expected -If you're encountering unexpected buried services meaning a lot of the trench has to be hand-dug for example, it may instead be reasonable to assume that there will be more services along the rest of the trench, meaning the chainage rate for the last 75% will be the same as the first 25%, and remaining duration should be 21d.


2) "Obviously on a large programme you can not ask PM remaining durations on each and every activity at the end of each reschedule."

Oh yes you can. For every activity that is IN PROGRESS on the update date, you need to satisfy yourself that you are confident of the remaining duration. This can be done by going at looking at the physical state of the works yourself (if you have enough experience), asking the person responsible for actually doing the work, or if there are no other options, asking the PM. This, along with collecting actual start & finish dates, is the fundamental bare bones of a schedule update. If you don't feel you have enough time to do this, you need to either get some help, work on less projects, or increase the interval between updates.


3) Systematic use of expected finish dates is an anathema to good scheduling practice. It effectively ignores all impacts of early or slow progress on the schedule. You may as well just draw up a "to do" list in MS Word.