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The myth of project float

Patrick Weaver
June 13, 2012

The concept of including ‘float’ in a project is less than 60 years old. The existence of a critical path and non-critical activities (with their associated ‘float’) grew out of the science of scheduling as defined by Critical Path Analysis (CPA) developed in 1957 by Kelly and Walker. Before this time, bar charts, milestones and industrial processes such as ‘line of balance’ were used to control projects. The key question is, if schedule float did not exist before 1957, how real is it today?

The tasks used to create the schedule are variable—different planners can/will choose different patterns of tasks to describe the same work—as are the allocated durations, based on presumed resources, and the interconnecting logic. Develop a ‘logic network’ using different assumptions and you generate different float values and a different ‘critical path’. Which option is real?

The finished schedule may look ‘logical’ and may represent the best intentions of the project team at the time it was developed, but it is not a vision of the actual future for the project as this cannot be foreseen. The schedule is only a presumed future that may happen if everyone works towards achieving the plan, and almost certainly won’t happen exactly as planned. Every deviation from the plan changes the float calculations!

Float is also ephemeral. The passage of time will of itself destroy ‘float’: float can only exist in the future, it cannot be stored and it cannot be recovered from past activities.

And finally, any changes that occur during the execution of the project that require changes in the project plan will frequently have dramatic effects on the location and amount of float in the overall schedule.

How float is created

The calculations that create the concept of float are precise and are typically processed in a computer. However, these very accurate calculations are based on assumptions, presumptions, and conjecture about what may happen in the future if the project team focuses on working to the project plan. Even with coloured lasers generating impressive outputs, the accuracy of the output data can never exceed the accuracy of the input data.

Probability theory reminds us that combining uncertainties reduces the probability of the output by the combined factors of the input. Float is precisely calculated in computer algorithms: the computer does not add to the uncertainty, but is based on the combination of a series of uncertain assumptions, and therefore remains uncertain. Importantly, we never know how uncertain until after the project is finished.

Unfortunately, the mathematical precision of critical path scheduling has caught the attention of lawyers and contract draftsmen leading to the evolving concept of the ‘contract program’ that confers a degree of legal certainty onto the schedule that cannot be supported by objective analysis. This approach has created the concept of ‘the contract program’, that can only be changed by agreement (if at all), and the assumption that only delays impacting the ‘critical path’ can give rise to extensions of time, delay costs, etc.

Since lawyers are no better at predicting and controlling the future than planners, all this type of rigid contract clause does is create a static means of measuring failure. The only beneficiaries are the lawyers and consultants who get paid to fight over claims made after the event—everyone loses.

Fortunately, accurate and useful are not synonymous. CPA is an extremely useful way of gaining insight to the essence of a project and when used properly can help to define an agreed way of working to achieve the project’s objectives, which in turn can help motivate and direct the project team. However, CPA is not an accurate or foolproof determinant of ‘the future’ regardless of the terms and conditions written into a contract.

And, as discussed above, every schedule is a creation of assumptions and presumptions crafted (with greater or lesser skills) by a planner and influenced by the algorithms built into the software used for analysis. A paradigm shift in thinking is required.

The art and science of planning

Recognising that ‘planning’ is a highly skilled, but imprecise art (supported by science) opens up a range of opportunities. Effective planning, based on this recognition, requires a willingness to continually monitor and adapt the schedule to make sure it represents the ‘best’ way forward based on the team’s current knowledge of the project supported by a cooperative approach to problem solving. Collaborating in the proactive management of the use of time is the best way to achieve the optimum project outcome that benefits the client and the contractor.

The ability to implement this collaborative approach requires a framework, a new form of contract and skilled ‘time managers’. The Chartered Institute of Building (CIOB) has embarked on a mission to deliver all three components supported by a ‘management education program’. The framework exists; a new form of contract is open for public review and training courses and credentials are under development. For a complete update on the ‘state of play’ see the briefing paper I presented to the CIOB centre in Shanghai.

Now to answer the question posed at the beginning: Is float real? Lawyers and people who believe in the perfect ‘contract program’ certainly believe float is real. My view is that float is a useful fiction. It is no more real than gravity, but in exactly the same way the Newtonian concept of gravity is useful for many things, the concept of float is useful in the management of projects. Ideas don’t have to be real to be useful!

Patrick Weaver
Patrick Weaver is the managing director of Mosaic Project Services and the business manager of Stakeholder Management Pty Ltd. He has been a member of both PMI and AIPM since 1986 and is a member of the Asia Pacific Forum of the Chartered Institute of Building. In addition to his work on ISO 21500, he has contributed to a range of standards developments with PMI, CIOB and AIPM.
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6 thoughts on “The myth of project float

  1. Patrick,
    Float exists and is real, just the same as 2 + 2 = 4 exists and is real.
    The whole idea of the project schedule/plan has been appropriated by lawyers to create a fiction of certainty and a “contract program” set in concrete at the start of a project. It is ridiculous but everyone, including people in the construction industry who should know better and who have been on the receiving end of the consequences, has been going along with it for decades. This myth undermines the valid intent of project planning and hijacks the worthy and ingenious critical path method for purposes it was never designed for. It ignores the assumptions and approximations and estimates that are necessary for project modelling. It ignores the FACT that any project plan is superseded by reality in a very short time and that the really essential thing is to have a planning method which responds to changes as quickly as possible and allows for constant, continuous re-planning as the project proceeds and as newer and better information becomes available.

    1. You have my sympathy Trevor,

      If you believe anything based on a series of guesses about possible future durations connected together by a series of simplistic assumptions about the way work may occur is ‘real’ you live in a very different world to most practical planners and mathematicians (even numbers are representations, they are not real).

      For the rest of us recognising every schedule model we develop is WRONG allows the key question of ‘how much error is acceptable for the model to still be useful?’ Useful and accurate are not synonymous!

      As Josh Billings said “It ain’t so much the things we don’t know that get us into trouble. It’s the things we know that just ain’t so!” Blindly believing the outputs from flawed models led to the GFC that almost wiped out the banks and is still causing major problems world-wide. The flaw in the model was not the problem, all models are wrong, it was the blind belief by banking managers that the models were accurate that prevented other checks and balances.

      Believing in ‘float’ typically has the same consequences for projects. Kelly and Walker were fully aware of the limitations in CPM, it’s a pity modern planners are not more aware of their tools strengths and weaknesses.

      1. Patrick,
        What’s real and what’s wrong, and whether things exist or not isn’t really the issue, is it?
        Sure, construction project plans (or programs, or schedules) are always models with lots of assumptions and approximations and estimates, as anyone who has done one knows. That in itself is not a flaw, but just a part of the planning process. Since we don’t have a choice (we can’t stop planning projects because the modelling isn’t perfect), then at least on the up side we have the critical path method, it’s better than anything else (what else?), we have the software to deal with the tedious arithmetic so that we can quickly try out alternative plans (different sets of assumptions and approximations and estimates). If it is all used properly, it all works as well as it can. It helps to squeeze out most of the uncertainty, and leave the remaining uncertainty as small as possible (but not zero). It gives us something to track.
        But like many other great ideas it is subject to being hijacked.

        1. Hi Trevor,

          I suggest you actually read the referenced materials!

          CPM is useful, what makes it dangerous is the idiocy of lawyers and others that expect planners to create a perfect schedule within a month of a major project starting and then the multi-thousand task ‘contract program’ somehow becomes an infallible statement of critical paths and float to be fought over after the project is finished late.

          The world is moving past this failed model towards the use of dynamic scheduling processes that are EXPECTED adapt to changing circumstances. The CIOB is leading this initiative, see:

          1. Patrick, I have already long ago read everything on your website and regularly check to see what’s new, and I own (and have read) both the PMI Practice Standard for Scheduling and the CIOB Guide To Good Practice in The Management Of Time In Complex Projects (what a mouthful!), both of which I bought from Mosaic.
            If the world is moving away from this current dysfunctional approach that we have been saddled with for years if not decades, it must be at a glacial speed because I have not seen evidence of it happening out there in the world of construction, where the standard forms of contracts and the legalistic idiocy that you mention is still deeply embedded. After all, there are plenty of people with a vested interest in it all going all wrong.

  2. The immediate opportunity to make a difference is on the CIOB website – they have developed a new form of contract focused on dispute minimisation and the proactive managment of time. Its open for public comment until the end of July:

    The combination of ‘the ‘CIOB Guide’, the contract and soon to be announced credentials for planners and schedulers are a foundation. Culture is also shifting, particularly in Australia with alliances, ECI and partnering becomming common.

    The momentum will come from everyone who understands the problem pushing for change.

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