Tag Archives: CPM

Time Analysis Schedule Calculations

There are a range of options for the calculation of dates and float in a CPM network.

I’ve just finished a White Paper focusing on the basic calculations and would appreciate comments on the correctness of the calculations and the methodology adopted.  The aim is to produce a definitive document that is generally agreed. 

You can download the paper from http://www.mosaicprojects.com.au/PDF/Schedule_Calculations.pdf   All comments gratefully appreciated.

Project Planning and Scheduling

The Guide to Good Practice in the Management of Time in Complex Projects (The Guide)  will be published at the end of this year. One of he key messages in The Guide is the need to separate planning from scheduling.

Project planning focuses on creating the project development strategy. It requires experience, vocabulary, communication and imagination and, at its highest level, provides the formula for the logistic strategy for the project construction. Project planning involves decisions concerning:

  • the overall strategy of how the work process is to be broken down for control;
  • how the control is to be managed;
  • what methods are to be used for design, procurement and delivery;
  • the strategy for subcontracting and procurement;
  • the interface between the various participants;
  • the zones of operation and their interface;
  • maximising efficiency of the project strategy with respect to cost and time;
  • risk and opportunity management;
  • the design for the schedule and its reports/communication plan.

Scheduling is a mixture of art and science to create the project manager’s time-allocation tool within the chosen software. It involves the interpretation of the results of project planning to ascertain, amongst other things, the start and finish dates of activities, their sequence and the required resources.

It is not good practice to plan the work whilst attempting to schedule it. Starting to develop the schedule before planning the project is unlikely to produce a satisfactory project-planning solution or an effective schedule.

This is not a new idea! James Kelley and Morgan Walker, the inventors of the Critical Path Method of scheduling in the very first paper published on the subject had the following to say:

A characteristic of contemporary project scheduling is the over-simplification which stems from the inability of unaided human beings to cope with sheer complexity. Even though we know that a detailed plan is necessary, we also know that management need only act when deviations from the plan occur. To resolve this situation we undertook to develop a technique that would be very simple but yet rigorous in application. One of the difficulties in the traditional approach is that planning and scheduling are carried on simultaneously. Our first step was to separate the functions of planning from scheduling.

This is an extract from the paper entitled Critical Path Planning and Scheduling delivered to the Eastern Joint Computer Conference in March 1959, by Kelley and Walker less then 2 years after they had invented CPM. Why is it 50 years later so many planners continue to ignore the wisdom learned from past projects and focus on entering data into computers before they have worked out the optimum way to deliver the project?

For more on the history of scheduling and an abstract of the Kelley and Walker paper see: A Brief History of Scheduling

PM History papers updated

Working on my paper for PMOZ 2010, Seeing the Road Ahead – the challenge of communicating schedule data  has required me to re-visit two key papers and augment them with new information and materials discovered in the last few years.

A Brief History of Scheduling – Back to the Future has had quite a lot of new materials incorporated. I am now confident this paper accurately lays out the development of scheduling and in particular, the origins of PERT and CPM.

The Origins of Modern Project Management  has had a few new footnotes included an links the development of modern project management to its roots the the spread of scheduling in the early 1960s.

Both updated papers are available for downloading and I have most of the reference materials available for anyone interested in further research into these topics.

The PMOZ paper will be available after publication in a couple of weeks. For more on the PMOZ conference see: http://www.pmoz.com.au/

Cause of Delay

Late last year the British High Court delivered a very interesting judgement on the assessment of delay, disruption and prolongation claims.

A delay to an activity may disrupt the work and it may delay the completion of the project. The two factors are independent (this is the fundamental principle in the UK Delay and Disruption Protocol).

In Costain Ltd v Charles Haswell & Partners Ltd [2009] EWHC B25 (TCC) (24 September 2009), the High Court has determined that for prolongation to occur, the actual delay has to flow through to a delay in the completion of the works. The mere fact the delayed activity was on the then critical path when it occurred is not of itself evidence the delay flowed through to the completion of the works. At paragraph 200(ii) the Justice Richard Fernyhough QC stated I find that it has not been shown by Costain that the critical delay caused to the project by the late provision of piled foundations to the RGF and IW buildings necessarily pushed out the contract completion date by that period or at all.

The fundamental issues relate to the definition of the critical path were canvassed inin my 2006  paper ‘Float is it real’.

At page 7 I argued:

Despite the CPM requirement for a single duration estimate, durations are variable; changing the estimate of a planned (future) duration or differences between the actual duration and planned duration on completed activities may change the critical path.

In the example above, at the ‘Initial Claim’ the critical path was running through the top chain of activities and ‘delay x’ was encountered. As no one can predict the future, at the time of the dealay it would be reasonable for everyone involved in the project to assume this is a critical delay and administer the contract accordingly.

Later, changes in the duration of the activities cause the critical path to move (either reduction in the time needed to complete some activities in the top chain or increases in duration in the lower chain, or both). When ‘delay y’ occurs as a ‘Later Claim’, this is also a critical delay based on the schedule at the time of the delay.

However, given the definition of the ‘Critical Path’ is: Generally, it is the longest path through the project. …that determines the duration of the project. The difficult question to answer is what happens to ‘delay x’, it appeared to be critical based on the best information available at the time the delay occurred. But changes over time (and after the time of the initial delay) have shown ‘delay x’ to actually be non-critical.

Certainly based on the Constain’s case, scheduling experts will need to define far more than simply a delay to an activity on the current critical path. As a minimum it will be necessary to show the delay impacted the overall completion and the extent of the impact. It will also be necessary to show the delay caused a general increase in costs for a prolongation claim to be sustained.