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Negative Float
Last Post 05 Jan 2012 08:16 AM by Jorge. 16 Replies.
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Henry León Posts:9

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05 Jan 2011 10:42 AM
    Dear Friends,
    A few weeks ago, I reviewed a schedule and find negative total float to many activities that the contractor can't explain.
    I think this was evidence about an error in logical relations by activities or constrains without justification betwen others, but in all cases it was an error.

    I expect any comment about if you can imagine any condition by justifi negative float.

    Kind Regards,

    Henry
    Stuart Miller Posts:7

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    14 Jan 2011 08:09 AM
    Scheduling tools are marvelous time savers, but the old saying about computers is still true "garbage in, garbage out". Or in this case more like, if you don't really understand the relasionship between tasks, you can get unexpected results.

    Vallid negitive float means the schedule is unrealistic and will fall behind/has fallen behind.

    The most common way, I've seen for having "apparent" negitive float is unrecognized concurrent activity.
    The second most common is estimates that are padded. I often employ a Critical Chain approach to time sensitive project; cutting all the padding out of individual tasks and providing the buffer time at key coordination points.

    The main thing is that scheduling tool results must be 'gut checked' by someone who understands the actual work involved.

    My, opition anyway ...Stu
    Donald LaPointe Posts:1

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    25 Jan 2011 08:40 AM
    To answer Mr. Leon's request for comments: I cannot think of any rationale that would "justify" negative float. There may be many explanations (risk identification and/or analysis didn't catch something, the risk owner (or others) didn't respond in time, etc.). If this was an identified risk, hopefully the response has been initiated and resolution is being achieved.

    I agree with Mr. Miller's assessment. PMs/PgMs must ensure they understand the tools being utilized. The organizations with which I have been associated all used MS Project. However, many problems that I inherited were the result of the previous PM/PgM not understanding Project's shortcomings and not being able to work around them.

    It can take many frustrating hours to reveal what truly caused the negative float. Unfortunately for Mr. Leon, it appears there may be some long nights ahead.

    Mr. Leon, I would recommend starting with your hypothesis that there "was...an error in logical relations by activities or constrains without justification between others." If this is the case, there may be bigger issues of which the negative float is only a symptom. The GIGO (Mr. Millers' 'garbage in, garbage out') may be with outdated, outmoded, or just plain out of left field organizational requirements for how schedules are developed. Having been involved in at least four efforts to change organizational processes AND if this is the case for Mr. Leon, this is an issue that needs to be researched, analyzed, and have alternatives recommended as soon as a TOTAL review of all project baselines, plans, artifacts, etc. is accomplished. It took me anywhere from 6 months to 3 years to effect the proper changes to "organizational process assets."

    Let us know what your discover and if any of us "SCoP" members can be of assistance!

    All the best,

    Don
    johnpmccarthy Posts:1

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    25 Jan 2011 10:15 AM
    Look for remaining duration in all prior predecessor activities. Current actual finishes may hide prior missing actual finishes. That remaining effort is still included in the total/accumulated remaining duration, possibly driving it to a negative total float result.
    Maaz Ahsan Posts:9

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    27 Jan 2011 01:53 AM
    Yes I completely agree with the possibility of negative float to exist in a schedule.

    Let us look at it not only with the fact that logic or linking has an error. After handling and maintaining schedules on complex fertilizer and oil & gas projects with multiple milestones I can firmly say that it is very common to see a negative float after a PROGRESS UPDATE. I am sure Mr. Henry was reviewing a schedule “updated with progress" from a Contractor. What all my friends have commented above is linked with the second step of schedule update which I can call as adjusting the future activities after progress update.

    To give an example, let us say that at Month 4 of a 1 Year Project, critical path activities have been delayed and as a result project end date has shifted. We should remember total float is linked with project end date. SO it was the responsibility of Contractor to re-adjust the schedule by using either of the two methods namely "Crashing" or "Fast Tracking" before submitting the schedule to Client. But this would consequently mean that the delay is caused by Contractor and hence it is His duty to mitigate the delay in future activities by either of the methods mentioned before. However in another scenario like one I had in my previous project, I was submitting my Client a schedule update with Negative float for many months hence proving that the project is going to get late. TO THIS every month my Client was not accepting the delay and requesting reasons for negative float and in response to that we prepared reasons to explain or as they say contractually we submitted a claim for disruptions in works due to Client. Extension of Time Claim is the next step to solve Negative Float issue (if reasons are attributed to Client) and I will share that finally we won almost 7 weeks extension. Hence Negative float disappeared with New Project End Date. This whole activity involves exhaustive work and supporting documentation.

    So in our case it seems Mr. Henry already asked the Contractor a reason for Negative Float and to my surprise as mentioned that Contractor couldnt explain is a pure example of poor implementation of Project Management Tools (specifically Scheduling Techniques) by Contractor. The advice should be to ask Contractor to re-adjust the schedule by putting more resources or doing parallel work hence bringing end date in line with baseline consequently removing Negative Float.

    Regards.

    Maaz
    Henry León Posts:9

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    28 Jan 2011 12:30 PM
    Thanks everybody by your comments. I can conclude that negative float is not acceptable condition in a schedule if this will be used as baseline or target. But in my specific case, it is a schedule to minning project as indicated by Maaz is a Schedule Control progress.
    In this condition, a schedule control progress and assuming the baseline schedule is Ok, without logic error o any other error, I think is better make a new baseline schedule. ¿what do you think?.

    Best regards,

    Henry
    Maaz Ahsan Posts:9

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    29 Jan 2011 09:12 PM
    If you are the Client, making a new baseline (with new end date) is purely your internal decision i.e. can you absorb the delay in project hence delay in productivity? etc. If yes, you can go ahead to change the baseline following the procedure Contract specifies. However if you are on the Contractor's side, to change the baseline needs approval from Client as it becomes a Contractual Document. So changing the baseline means an amendment to a Contract Document hence it has to be agreed with Client/Engineer.

    regards.
    ranjansil Posts:1

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    25 Mar 2011 10:51 PM
    Hello Friends,

    Forgive me ! .... but it maybe a digression to the above topic

    Let me know your opinion to the pass the PMP exam cleverly .... I completed some of the topic, then there was a gap (due to work pressure & moving outstation consequently), then again came back reading different topics and in the process missed the logical flow and had to start all over again resulting in repeat effort

    Thanks for your time
    Dhrritie
    psturdivant Posts:1

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    27 Mar 2011 10:19 AM
    Dear friends,

    This is an interesting, and, a topic which has been debated with some intensity. In my opinion, it's a matter of perspective; that of owners or contractors; a tool or a hammer. But whichever side you are on, it is important to remember that activity durations are estimates.

    Many of reasons given for logic erros, etc. are valid sources to be examined. Once those factors are eliminated, from a contractor point of view, there are valid reasons to show negative float. The first and foremost, it is an accurate representation of where you are on the project. In this case, negative float is a valid condition. As you make adjustments in resources or apply alternative methodologies, you can witness the changes, over time, to evaluate the effective of various remedies. The second valid reason for negative float is to validate conditions which may well be the responsibility of the someone else on the project. A claim is not necessarily a negative term. It is simply the recognition of an existing condition. Who pays and why is a different matter, that needs to be treated separately.

    In my experience, at the heart of the refusal by an owner to accept a schedule with negative float is either the lack of managerial maturity, or the overt attempt to quash the documentation of a valid claim. In both cases, it is the responsibility of the project manager to step up to the plate to defend their position, and the entity they are charged with protecting.

    A schedule can be utilized as a tool of planning, or a hammer of tyranny. Are you managing the project, or managing the (scheduling) process? This is often the source of the rub. What is your perspective?

    Best regards,

    Peter Sturdivant
    Maaz Ahsan Posts:9

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    06 Apr 2011 12:04 AM
    [quote]
    Posted By ranjansil on 26 Mar 2011 01:51 AM
    Hello Friends,

    Forgive me ! .... but it maybe a digression to the above topic

    Let me know your opinion to the pass the PMP exam cleverly .... I completed some of the topic, then there was a gap (due to work pressure & moving outstation consequently), then again came back reading different topics and in the process missed the logical flow and had to start all over again resulting in repeat effort

    Thanks for your time
    Dhrritie
    [/quote]

    Dear Ranjansil,

    As you mentioned yourself, this is not the right place to discuss this. I would advice you that since you are a member of PMI, you should join one of your local chapter (for your city) and create a new discussion there or join one.

    However the key to success is continuous study from PMBOK before taking the exam.

    Rgds,

    Maaz
    BrianDMorgan Posts:5

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    07 Apr 2011 06:58 AM
    Hi, looking at the updates from Henry on Jan 28 and Maaz on Jan 30, I would ceratinly consider recreating the baseline in exceptional cisrumstances and on the basis that there is agreement from stakeholders to do so. It does sound like whatever problems were in the plna / baseline originally have impacted on the "true picture", but there are downsides to just creating a new baseline as this can then give a false view of the situation and can sometimes be seen as hiding the problem (which I don't think Henry is trying to do).
    Henry León Posts:9

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    07 Apr 2011 05:40 PM
    DEar Friends,
    Let me to update about how we resolved this.
    Later to many meeting to discuss this problem, the Owner Team and our Contractor decide to re-baseline the Master Schedule according to Recovery Plan.

    In this experience, clearly, no exist any way to accept negative float in the schedule, and this was a warning in the project that requested an especific analysis to identifi problems in our project, using this indicator to validate the logic of schedule and detect the activities that we need to accelerating or execute in same time with others in a fastrack strategy.

    So in this circunstances the original schedule baseline is not the better to show how we were solving the delays in the project.

    Kind Regards,

    Henry
    cmogasha Posts:1

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    03 May 2011 12:29 AM
    In Ms Project you will get negative float if you set a deadline that is before the current completion date. And this makes sense if you start your backpass calculation from teh date of teh deadline and not the current end date. Interpretation. The project cannot be completed in time by the value of the negative float.
    Patrick Weaver Posts:10

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    22 May 2011 02:29 AM
    Arguing about ‘float’ is pointless. Negative float can only exist if there is a date constraint in the schedule. Sensible tools require an overt action on the part of the scheduler to impose a constraint, the more popular ‘amateur’ tools will add constraints as the tool thinks appropriate.

    The question to ask is where the constraint is, and is it reasonable? If the constraint represents a contract obligation, the negative float shows the degree of difficulty in meeting the obligation (or highlights errors in the schedule logic). If the constraint is meaningless remove it and the negative float disappears.

    To understand more about the limited value of ‘float’ see: http://www.mosaicprojects.com.au/PD..._Float.pdf
    Maaz Ahsan Posts:9

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    09 Oct 2011 04:47 AM
    Thanks Henry for updating how you solved the issue. Just like I have experienced also; your client did the same.

    @Patrick, although you are right about the fact that constraints in the schedule can create a critical path when you update the schedule. But you should also remember that when you assign a baseline to your working schedule your end date is considered as the end of the project. It cannot be said that there is not critical path in the project (zero or negative float) since then it is not a project but a process.

    One cannot remove the negative float byt just removing constraints; there are many precautionary measures we need to take while removing the negative float. Like I said before we can crash or fast track depending upon the possibility. It is never useless to discuss the float NOR we can say it is an insignificant factor in a planning. It is the most important factor for a Project Manager to know the criticality. I think it is one of those things which a PM should always have in his mind to observe the critical path and take necessary actions to keep it in control.
    Patrick Weaver Posts:10

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    01 Jan 2012 01:22 AM
    Whilst your comments reflect many sets of contract conditions Maaz, I believe you are completely wrong and the approach you offer can only enhance the prospect of project failure.

    Float is not a definer of the critical path under any circumstances.

    The only constraints in a schedule should be real constraints imposed by the contract or some external inevitability (for the last 40 years I have always advocated that any constraint worth putting in the schedule is worth putting on a Milestone so it stands out – there should never be more then 2 or 3).

    The base line may, or may not finish on the contracted completion date – sensible schedules plan to finish early to provide contingencies. I’ve known schedules to be rejected because the minimum float value was less than +30 days (the client wanted a sensible contingency in the baseline).

    Crashing is only possible if you can effectively deploy more resources and inevitably increases costs and risks (and only occasionally works in the real project unless the project was understaffed in the first instance).

    Fast tracking inevitably increases the number of resources deployed and increases risks but does tend to be more successful if done well.

    If the negative float is real, caused by a real constraint that is properly documented (not the situation described in the original post) the only effective way to manage the situation is to review the way the work is being done and see how you can change this to optimise the use of the available resources to achieve the contracted objectives. ‘What-If’ in consultation with the project workforce.

    Remember, the original set of guesses about the future workings of the project embedded in the schedule is simply a bunch of assumptions about what might happen and how. These can and should be changed on a regular basis to keep the schedule as accurate as possible – no one alive in at least the last 2000 years has been able to predict the future, including all of the lawyers who write contract clauses.

    Crashing and Fast Tracking are very simplistic options that are easy to change when playing in the software and don’t work in reality. If they did projects would finish on schedule; most don’t. Unfortunately playing games with the model in the software may make a pretty picture but in reality this solves nothing.

    What has to change is how the work is actually being done by the actual resources working on the project. To learn a bit more about this first see: Scheduling in the Age of Complexity (Sixth Annual PMI College of Scheduling Conference presentation) - http://www.mosaicprojects.com.au/Re...s_089.html

    Then: Resource optimisation - a new paradigm for project scheduling http://www.mosaicprojects.com.au/Re...s_152.html This paper will be available after presentation at the conference in May, some initial work is on the website.
    Jorge Posts:2

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    05 Jan 2012 08:16 AM
    Regarding the possible existence of negative float. Of course negative float is just as possible a condition as having positive float is. It is just saying that the time remaining does not support the time required to complete the amount of work remaining, at least not along the the longest pole, i.e. critical path. It is one reason we plan in the first place - in order to be able to forecast when such a condition exists and put into place a revised plan to mitigate the condition. The earlier your recognize you have negative float, or have a trend in that direction, the more solutions are available. And those solutions are usually more effective, cheaper, and easier to implement the earlier the better. Understanding the most effective way of correcting negative float is a bit of an art once you understand that float is a property of the path - not of any given activity in that path. Being able to adjudicate negative float by crashing or fast-tracking in the least disruptive way is the goal. Arbitrary slashing of activity durations in the critical path is the least desirable solution if original durations are to be believed - doing so just converts total float into increased risk - with the likelihood of success being diminished. It is an iterative process to be sure.
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