Category Archives: Scheduling

Project planning and scheduling posts

Everything old is new again – especially when there is a $ to be made………..

Following on from a post by Raphael M Dua (Raf) in LinkedIn, the number of people posting about their ‘new’ way to solve project scheduling and controls issues seems to be expanding.  The problem is most of their claims are false and misleading.

Some of the most frequent claims are around lean construction management the advocates claim they can solve your project scheduling problems (for a fee) because:

  • Lean construction management has introduced the concept of using input from the first line supervisors to plan the work. While this is a really good idea it is far from ‘new’….  Go back to 2009 and the concept of ‘last planner’ was floating around (and making the same claims), see The Last Planner and other Old Ideas.  Go back even further to the 1970s and major construction companies such as Bechtel and Fluor were applying schedule levels. The Level 5 schedules were short-term ‘look-ahead’ schedules developed every couple of weeks that considered in detail the work for the next month.  These schedules were developed by the foremen and subcontractors responsible for the work, based on the resources available on site to do the work. See more on Schedule Levels.
  • Lean construction management considers resource availability and CPM cannot analyze resources. This is a blatant lie. Every CPM scheduling tool from Microsoft Project to Primavera has the capability to analyze resource. Most have multiple options for scheduling activities against resource availabilities. The image is from a Primavera (P6) training course.  The simple fact is CPM scheduling tools have included resource levelling since the mainframe scheduling tools of the early 1960s.

I’m not sure if the proponents of lean construction making these claims are simply ignorant of the existing capabilities, or making dishonest claims for commercial gain.  But the problems they are claiming to solve are significant and won’t be helped by this type of false narrative.  The core issues appear to be:

  1. A large number of CPM schedules don’t include resources and the projects fail (the USA GAO is addressing this by demanding a resource loaded schedule on all government projects above a defined size). The root causes are untrained schedulers (being taught how to run software is not the same as teaching people how to be effective schedulers….) and the contractor’s management being unwilling to invest in developing the skills and allocate the time and resources needed to develop a comprehensive resource loaded schedule.
  2. The inability of main/head contractors to rely on subcontractors supplying adequate levels of resource at the time needed. This is a price and supply chain issues that has been around for decades – see the Latham report from 1994.
  3. The lack of improvement in resource management techniques for the last 40+ years – there are better options than CPM scheduling, see Resource Optimization at:

Until people actually address these core issues spending money on another fad solution won’t change anything.

I cannot do much to solve the cultural issues outlined above, but my Book Easy CPM goes a long way towards providing the knowledge framework needed to develop a skilled scheduler after they have learned to drive a scheduling tool:   

Critical Path Scheduling – 4 Things People Don’t Get

Over the last few weeks, I’ve seen more rubbish published about CPM from supposed experts than usual.  The false assertions range from statement claiming CPM does not include resource analysis to ones confusing basic resource scheduling processes.

So here are a few supported facts:

  1. The Critical Path Method (CPM), and PERT (Program Evaluation and Review Technique) both started out as ‘activity-on-arrow’ networks in 1957. The Precedence Diagramming Method (PDM) uses an activity-on-node’ notation, and was published in 1962 as a manual technique but was quickly applied to both PERT and CPM networks by the computer companies developing CPM and PERT software (by 1965 everything had merged into ‘all encompassing’ software packages). See:
  2. The two fundamental differences between CPM and PERT are:
    1. CPM uses a single deterministic duration estimate, PERT uses three duration estimates and is used to assess the probability of achieving a milestone.
    2. CPM was built to resolve resourcing issues on plant shutdowns for Du Pont, PERT/Time did not include resources until the introduction of PERT/Cost in 1961. PERT/Cost used a single resource estimate. See:
  3. Resource analysis uses time analysis calculations as a basis for its resource calculations:
    1. Aggregation: sums the resource requirements per day based on time analysis dates (usually early start)
    2. Smoothing: levels resource demand by using the available float. Some resource overloads will be reduced or eliminated by using float to shift non-critical activities back in time. The project end date and other constraints do not change, which means in some situations resource overloading may still occur.
    3. Leveling: delays critical tasks and the project completion to avoid overloading. See:

The ‘lean construction’ salesmen promoting the lie CPM does not include resources are simply wrong. What is true are a lot of schedulers develop schedules without resources, resource balancing in a CPM schedule is difficult, and there are now better options for resource optimization available in some tools. But many contracts and the USA GAO require resource loaded schedules.  Similarly, there are a number of ‘experts’ confusing resource smoothing and levelling (there seems to be quite a few). To correct their error, all they need to do is simply read a standard – the PMBOK® Guide (6th Ed.) is a good starting point and is consistent with all other credible authorities for the last 50+ years.

  • The purpose of a CPM schedule is also confused by many experts. Every schedule is a simple model of how work on a project may unfold in the future. This means the schedule cannot be completely accurate:
    • The schedule is a simplified representation, it contains a few hundred, or thousand activities that summarize the millions of actions that the project team will actually do to complete the work.
    • Every duration and resource estimate is an assessment of what may happen in the future. The unknown is the degree of error in each estimate, and overall.
    • The project team may, or may not, follow the planned sequence of work.

So, what’s the point of developing a schedule?  As Prof. George Box pointed out in “Time Series Analysis – Forecasting and Control” (page 285): “All models are approximations, and no model form can ever represent the truth absolutely. Given sufficient data, statistical tests can discredit models that could nevertheless be entirely adequate for the purpose at hand. Alternatively, tests can fail to indicate serious departures from assumptions because of small sample sizes or because these tests are insensitive to the types of discrepancies that occur. The best policy is to devise the most sensitive statistical procedures possible but be prepared to employ models that exhibit slight lack of fit. If diagnostic checks, which have been thoughtfully devised, are applied to a model fitted to a reasonably large body of data and fail to show serious discrepancies, then we should feel comfortable using that model.”  This and a number of similar quotes by him are often paraphrased as ‘All models are wrong, but some are useful’. A well-constructed CPM schedule can be extremely useful if it is used to:

  • Obtain agreement from the project team and resource suppliers on how the work will be done,
  • For assessing risk and identifying issues early,
  • Measuring performance against the plan and identifying variances,
  • Testing options to overcome negative variances and then obtaining buy-in to implement the recovery action.

But the CPM schedule will only be useful, if it is used by the project team to communicate, agree, and coordinate their work. The bigger the project, the more important this communication, agreement, and buy-in becomes. This is a dynamic, adaptive, agile, process. Focusing on what was thought to be a good idea last year embedded in a fossilized ‘contact program’ that does not change may keep claims consultants in a job, but it won’t help finish the project on time. If the schedule is not working on your project, it is a management and skills issue, changing to a different tool will not solve either of these factors.

One of my objectives in publishing Easy CPM was to make a low cost, easy-to-read resource available to schedulers who want to lift their skills – fixing management is a more interesting challenge. For more on Easy CPM see:

Finally, to answer the last question, borrowing from Group Captain Sir Douglas Bader: “Schedules are for the guidance of wise people and the obedience of fools!”  They provide insight, not control, and can be extremely useful if they are used!

CPM Anomalies Invalidate Monte Carlo

A couple of weeks ago I posted on some of the anomalies in CPM logic that will cause unexpected results: CPM Scheduling – the logical way to error #1. A comment on the post by Santosh Bhat started me thinking about the effect of these logical constructs on risk analysis.

The various arrangement of activities and links shown in CPM Scheduling – the logical way to error #1 (with the addition of a few more non-controlling links) follow all of the scheduling rules tested by DCMA and other assessments. The problem is when you change the duration of a critical activity, there is either no effect or the reverse effect on the overall schedule duration.

In this example, the change in the overall project duration is the exact opposite of the change in the duration of Activity B (read the previous post for a more detailed explanation).  For this discussion, it is sufficient to know that an increase of 2 weeks in the duration of ‘B’ results in a reduction of the overall project duration of 2 weeks (and vice-versa).

The effect these anomalies on the voracity of a Monte Carlo analysis is significant. The essence of Monte Carlo is to analyze a schedule 100s of times using different activity durations selected from a pre-determined range that represents the uncertainty associated with each of the identified risks in a schedule. If the risk event occurs, or is more serious, the affected activity duration in increased appropriately (see more on Monte Carlo). 

In addition to calculating the probability of completing by any particular date, most Monte Carlo tools also generate tornado charts showing the comparative significance of each risk included in the analysis and its effect on the overall calculation.  For example, listing the risks that have the strongest correlation between the event occurring and the project being delayed.  

Tornado charts help the project’s management to focus on mitigating the most significant risks.

When a risk is associated with an activity that causes on of the anomalies outlined in CPM Scheduling – the logical way to error #1 the consequence is a reduction in the accuracy of the overall probability assessments, and more importantly to reduce the significance of the risk in tornado charts. The outcome of the anomalous modelling is to challenge the fundamental basis of Monte Carlo. There are more examples of similar logical inconsistencies, that will devalue Monte Carlo analysis, included in Section 3.5 of Easy CPM.

Easy CPM is designed for schedulers that know how to operate the tools efficiently, and are looking to lift their skills to the next level. The book is available for preview, purchase (price $35), and immediate download, from:

CPM Scheduling – the logical way to error #1

Section 3.5 of Easy CPM looks at some of the logical scheduling errors that are easy to introduce into a schedule, and that for the most part will not show up in the automated checking tools applying test such as the DCMA 14 point assessment (see more on the DCMA assessment at:

The naming convention used below is borrowed from Miklos Hajdu.  In all cases the links shown in the diagram are the controlling links, in a ‘live’ schedule there are likely to be many other links as well.

Reverse Critical

In this logical configuration, the change in the overall project duration is the opposite of any change in the activity duration.

A reduction of 1-day in the duration of activity B will lengthen the project duration by one day, an increase of 1-day will reduce the project duration by one day.

Neutral Critical Open ends (dangles) have the effect of isolating the activity duration from the schedule. The project duration is unaffected by either a 1-day decrease, or a 1-day increase in the duration of activity B. There are two variants, SS and FF:

In both cases it does not matter what change is made to activity B, there is no change in the overall duration of the project.  This is one of the primary reasons almost every scheduling standard requires a link from a predecessor into the start of every activity and a link from the end of the activity to a successor, however, even with other links in place, if the control is through either of the scenarios above, the result is still the same.

Bi-critical Activities

Finally, for this post, any change in the duration of activity B will cause the project duration to increase.

A 1-day reduction of the duration of activity B will lengthen the project duration by one day, and an increase of 1-day will also lengthen the project duration by one day.  Bi-critical activities depend on having a balanced ladder where all of the links and activities are critical in the baseline schedule. Increasing the duration of B pushes the completion of C through the FF link. Reducing the duration of B pulls the SS link back to a later time and therefore delays the start of C.  The same effect will occur if the ladder is unbalanced or there is some float across the whole ladder, it is just not as obvious and may not flow through to a delay depending on the float values and the extent of the change.

Easy CPM

There are more examples of similar logical inconsistencies included in Section 3.5 of Easy CPM. Easy CPM is designed for schedulers that know how to operate the tools efficiently, and are looking to lift their skills to the next level. The book is available for preview, purchase (price $35), and immediate download, from:  

Easy CPM launched

Easy CPM is a self-paced course-in-a-book, supported by Mosaic Project Services Pty Ltd, focused on developing and using an effective schedule in almost any software tool. For projects using EVM, Easy CPM acts as a companion to our Easy EVM focusing on developing the realistic and achievable schedule that underpins EVM and is needed for the successful delivery of all projects.

The book is intended to provide practical guidance to people involved in developing, or using, schedules based on the Critical Path Method (CPM). It is designed to act as a reference and practice guide to enhance the effectiveness of their scheduling practice after they have learned to use the CPM scheduling software of their choice.

The basic premise underpinning the development of this book is that a schedule is only useful if it is used. Creating a usable schedule requires two parallel processes:

  1. It requires a pragmatic approach to planning and scheduling the future work of a project to create a realistic and achievable schedule.
  2. It also requires management to make effective use of the schedule, which is a management challenge that typically involves a significant shift in culture and expectations.

Both of these aspects are considered in Easy CPM.

The book is divided into six sections, each section includes guidance on an aspect of CPM scheduling, references, and a set of 20 questions; with the answers in Section 7. Section 8 incorporates the appendix.

$35.00 AUD (Plus GST, Australian customers only). Size: 295 pages, 120 questions, file size 22 Mb.

Preview Easy CPM on Book2Look, or click through for more information and to buy.

See more on Easy EVM.

Scheduling Core Papers Updated

We’ve been working on a series of books:
Easy EVM is published: See more on the book
Easy CPM is a work in progress, publication later this year
Easy SHM will follow in 2022.

As part of the development of Easy CPM as course-in-a-book which is designed to act as a reference and practice guide for people implementing CPM scheduling after they have learned to use the CPM scheduling software of their choice. We have updated Mosaic’s ‘core scheduling papers‘; these are:
A Guide to Scheduling Good Practice
Attributes of a Scheduler
Dynamic Scheduling
Links, Lags & Ladders
Schedule Float
Schedule Levels
Schedule Calculations

These updated papers are available to download and use free of charge under a Creative Commons 3.0 license: Download the papers from

Philosophies & Principles Used to Shape Planning Approaches

Any output from a planning process is a consequence of the approach applied by the planner to develop their plan.  Different people will develop different plans to achieve the same objectives based on their knowledge, experience and attitudes. This influence can be ignored or, if better understood, exploited!

This article outlines the fundamental principles and philosophies that can be used by planners to develop their plan:

For more papers on schedule strategy and design see:

The Origins of Schedule Management

FEM MagazineOur peer-reviewed paper, ‘The origins of schedule management: the concepts used in planning, allocating, visualizing and managing time in a project’ has recently published in the ‘Frontiers of Engineering Management’ at:

This paper brings together a number of published articles and other research we’ve undertaken in the last decade or so to present a coherent view of the evolution of project scheduling in a format that can be used by other Academics.  It is also aimed at correcting many of the commonly held misconceptions around this topic.

The concepts used for project schedule management have very deep roots; getting the right people in the right place at the right time to accomplish an objective has been a major organizational challenge for at least 3000 years! In ancient times this process seems to have been based on the scheme of arrangements being contained in the leader’s mind and instructions communicated verbally. Modern approaches to solving the twin challenges of first thinking through the ‘plan’ and then communicating the plan to the people who need to do ‘the right work, at the right time, in the right place’ use sophisticated graphics, charts, diagrams, and computations, but the problem and challenges are the same.

This paper traces the development of the concepts most project managers take for granted including bar charts and critical path schedules from their origins (which are far earlier than most people think) through to the modern day. The first section of the paper looks at the development of concepts that allow the visualization of time and other data. The second looks at the shift from static representations to dynamic modelling through the emergence of computers, dynamic calculations and integrated data from the 1950s to the present time.

You can download an augmented version of the paper from:

Project scheduling Update

1. A new paper looking at the origins of CPM has been uploaded to our PM-History page – looks at where the concepts that evolved into CPM and PERT originated. All of our papers can be found at:

2.  The PMI members’ only Scheduling Conference 2017 is going to be great! Over 17,000 people are registered already – I’m the last speaker for the day (which means I only have to get up at 6:00am Australian time to participate…..) More information see:  My topic looks at the effect of the data generated by BIM, drones and other technology on controls.

3.  PGCS Canberra is on in early May – too good to miss, see:

Setting up a project controls system for success

A couple of hour’s hard thinking can make the difference between project success and failure!  Far too many projects are simply started without any real thought as to the best strategy for delivery and what control systems are really needed to support the management of that delivery – one size does not ‘fit-all’ and simply repeating past failures creates more failures.  Similarly, far too many control systems are implemented that simply generate useless paperwork (frequently to meet contractual requirements) when what’s needed is effective controls information.

Remembering that all project controls documents have to be used and maintained to be useful; the three key thinking processes needed to help build project success are:

  • First the big question – how are we going to do the work to maximise the opportunity of success and optimise risk??  This is a strategic question and affects procurement as much as anything – off-site assembly needs a very different approach to on-site assembly. This does not need a complicated document but the strategy does need to be agreed; see:
  • From the strategy, the project management team structure can be designed to best manage the work as it will be accomplished and these people (or at least the key people) can then contribute to the planning process. Pictures are as useful as anything to define the overall flow of the work; see:
  • Once you know the way the work will be accomplished and the overall flow/sequence of the work you are now in a position to plan the project controls function aiming to apply the minimum amount of ‘controls’ necessary to be effective.  Excessive controls simply waste money and management time. My approach is always to do a bit less then I think may be needed because you can always add some additional features if the need eventuates – it Is nearly impossible to remove controls once they have been implemented.
  • Then you can develop the schedule and other control tools needed for effective management working within the framework outlined above.

This area is what PMI call Schedule strategy and Schedule planning and development. Getting this ‘front-end’ stuff right is the best foundation for a successful completion of a project; this is the reason these elements of project controls have a strong emphasis in the PMI-SP exam.

Conversely, stuffing up the strategy in particular, means the project is set up to fail and implementing control systems that do not support the management structures within the project simply mean the controls people are wasting their time and the time of everyone they engage with.

However, creating a project that is based on a sound strategy supported by a useful project controls system will require some cultural changes:

  • The project manager and project executive will need to take some time to look at strategic options and develop an effective delivery strategy.
  • The organisation and client will need to allow the project controls professionals to work through the challenges of developing a ‘light-but-effective’ controls system and then review/approve the system – this is more difficult than simply requiring every project to comply with some bloated standard controls process that no one uses (except for claims) but should deliver massive benefits.
  • The organisation will need skilled project controls professionals……….
  • And the project management team will need to be willing to work with and use the project controls.

The problem is easy to outline – fixing it to enhance the project success rate is a major challenge.