Float - Is It Real?
business is so valuable as time."
John H. Patterson
Keywords: Schedule, Control, CPM, Float, Updates.
Float - Is It Real? [P043]
The concept of ‘float’ is less than 50 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). In 1956/57 Kelley and Walker started developing the algorithms that became the ‘Activity-on-Arrow’ or ADM methodology. Before this time, Gantt Charts, milestones and industrial processes such as ‘line of balance’ were used to control projects. From the 1960s onwards, the use of ‘critical path’ techniques began to dominate. [ See: A Brief History of Scheduling - Back to the Future ]
Unfortunately, the mathematical precision of critical path scheduling also caught the attention of lawyers and contract draftsmen leading to the evolving concept of the ‘contract program’ and conferring a degree of legal certainty onto the schedule that cannot be supported by objective analysis. Whilst CPA is an extremely useful way of gaining insight to the essence of a project and it helps define an agreed way of working to achieve the project, CPA is not an accurate or foolproof determinant of ‘the future’. Every schedule is a creation of assumptions and presumptions crafted (with greater or lesser skills) by a scheduler and influenced by the algorithms built into the software used for analysis. The tasks used to crate 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. [ See: The Cost of Time - or who's duration is it anyway? ]
The schedule may look ‘logical’ and may represent the best intentions of the project team at the time it is developed, but it is not the actual future (this cannot be foreseen). The schedule is only a presumed future that may happen, and equally, may not. The effluxion of time will of itself destroy ‘float’, and any changes that occur during the execution of the project can have dramatic effects on the overall schedule.
Other planning presumptions are equally doubtful. ‘Overloaded’ resources are impossible; a resource can only work for 60 minutes in an hour, even if the scheduling tool is showing 90 minutes work is required! Similarly, ‘under-utilised’ resources are rarely seen; most committed team members will find something useful to do even if this means blurring and re-shaping the neatly defined tasks included in the schedule.
However, recognising that ‘scheduling’ is an imprecise art (supported by science) opens up a range of governance problems. Effective scheduling, 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. A ‘legal’ view of effective project governance (particularly given the potential size of delay, disruption and prolongation claims) tends to require more certainty and focuses on risk mitigation. This view 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.
This paper analyses the factors creating the ‘critical path’ and ‘float’ within a schedule and then look at ways of resolving the conflicting views outlined above. Potential solutions to be canvassed include the UK ‘Delay and Disruption Protocol’, client led integrated teams and the use of alternative planning methods such as location based scheduling, trend analysis and earned schedule.