I’m wondering what is causing the confusion appearing in so many posts lately concerning the definition of the critical path. Is it:

1. A lack of knowledge?
2. People being out of date and using superseded definitions?
3. People not understanding the difference between a characteristic and a definition?

As most people know (or should know) the definition used by the PMI Practice Standard for Scheduling (Third Edition), the International Standards Organization (ISO) and most other reputable authorities in their standards is similar to:

Critical Path: sequence of activities that determine the earliest possible completion date for the project or phase. 

For more on the development of this definition see: Defining the Critical Path.

To deal with the questions above, in reverse order:

The difference between a characteristic and a definition.

The definition of a phrase or concept (the ‘critical path’ is both) should be a short, concise, statement that is always correct. A characteristic is something that indicates the concept may be present.

Everyone of significance has always agreed the critical path is the sequence of activities determining the earliest possible completion of the project (or if the project has staged completions, a stage or phase).  This is the basis of the current valid definitions. As a direct consequence of this in a properly constructed CPM schedule, the float on the critical path is likely to be lower than on other paths but not always. Low float or zero float is a characteristic that is often seen on a critical path, but this is a consequence of its defining feature, it being longer than other paths. 

Superseded definitions.

In the 1960s and 70s, most CPM schedules were hand drawn and calculated using a day number calendar. This meant there was only one calendar and constraints were uncommon.  When there are no constraints and only a single calendar in use, the critical path has zero float! From the 1980s on, most CPM schedules have been developed using various software tool, all of which offer the user the option to impose date constraints and use multiple calendars (mainframe scheduling tools generally had these features from the 1960s on).

Using more than one calendar can cause different float values to occur within a single chain of activities, this is discussed in Calendars and the Critical Path.  

Date constraints can create positive or negative float (usually negative) depending on the imposed date compared to the calculated date and the type of constraint, this is discussed in Negative Float and the Critical Path.

Consequently for at least the last 40 years, the definition of a critical path cannot be based on float – float changes depending on other factors.

Knowledge?

One of the problems with frequently repeated fallacies is when people do a reference search, they find a viable answer, and then use that information assuming the information is correct. This is the way we learn, and is common across all disciplines.

Academic papers are built based on references, and despite peer review process, can reference false information and continue to spread the falsehood. One classic example of this is the number of books and papers that still claim Henry Gantt developed the bar chart despite the fact bar charts were in use 100 year before Gantt published his books (which make no claim to him having invented the concept), for more on this see: https://mosaicprojects.com.au/PMKI-ZSY-020.php#Barchart. Another common falsehood is Henry Gantt ‘invented project management’ – his work was focused on improving factory production processes: https://mosaicprojects.com.au/PMKI-ZSY-025.php#Overview

Academics are trained researchers, and still make mistakes; the rest of us have a bigger challenge! The spread of un-reviewed publications via the internet in the last 20+ years started the problem. Now Generative AI (Gen AI) and large language models (LLM) are exacerbating the problem. For most of us it is getting harder and harder to understand where the information being presented a person, or in an article originated. Gen AI is built to translate data into language, it has no ability to determine if the data it has found is from a credible source or not. And as more and more text is produced by the various Gen AI tools the more often wrong information will be repeated making it more likely the wrong information will be found and repeated again, and again.   

I’m not sure of the solution to this challenge Gen AI is clearly not skilled in project management practice (even the PMI AI tool), for more discussion on this important topic see: https://mosaicprojects.com.au/PMKI-SCH-033.php#AI-Discussion  

Reference

One reference that is reliable is Mosaic’s Easy CPM.  It incorporates most of what we know, focused on  developing and using an effective schedule in any software tool. The book is designed to provide practical guidance to people involved in developing, or using, schedules based on the Critical Path Method (CPM), and act as a reference and practice guide to enhance the effectiveness of their scheduling practice.

For more see: https://mosaicprojects.com.au/shop-easy-cpm.php 

The question posed in this short post is how can we fulfil this objective when different processes calculate completely different completion dates for the same set of project data?  The options for the calculated project delay for the simple project outlined above are:

–  CPM using progress override calculates a 3 week delay.

–  CPM using retained logic calculates a 4 week delay.

–  WPM and ES calculate a 16 week (4 month) delay.

Which option is correct or are all of the options correct and project managers are free to choose the delay they prefer to report?  Full details of the various options are included in Calculating Completion: https://mosaicprojects.com.au/PDF_Papers/P217_Calculating_Completion.pdf

My suggestion is a realistic prediction of completion needs more than a simple CPM update that assumes all future work will miraculously be completed as planned. WPM (Work Performance Management) has been developed to apply a similar approach to EVM, ES and ED, based on understanding the ratio between work performed and work planned and applying this factor to the future incomplete work to assess the likely completion date if nothing changes.

For more on WPM see: https://mosaicprojects.com.au/PMKI-SCH-041.php#WPM  

[1] See Project Controls – A Definition: https://mosaicprojects.com.au/WhitePapers/WP1093_Project_Controls.pdf

Calculating a projected project completion date is subjective! Depending on the tools used for assessing the status, and predicting the completion, of this simple project the assessment can vary from:

• We don’t really know,
• The work is currently behind schedule but we are not sure by how much,
• The work is 5 weeks, 1 month, or 3 weeks late, or
• The project completion is expected to be either 3 weeks, 1 month or 4 months late!

The answer depends on the tool you are using, and the way it is used.

Our latest paper, Calculating Completion, uses the simple project shown above to assess the subjective and objective information available from: Bar Charts, Burndown Charts, Kanban Boards, Velocity, CPM, EVM + ES, and Work Performance Management (WPM). It explains the way the results are derived by each of the tools and the options open to users to vary the result.

The challenge for project controls experts, is all of the answers above can be realistically extracted from one or more of these tools! Deciding which option is correct is an altogether more complex question, there probably is no single correct answer!

To read more on this challenge, download Calculating Completion, from:  https://mosaicprojects.com.au/PDF_Papers/P217_Calculating_Completion.pdf

For more on Project Controls see: https://mosaicprojects.com.au/PMKI-SCH-005.php

• Updates to some of our pages focused on construction and engineering:
  – Construction Management
  – Building Information Modelling (BIM)
  – Dispute Management
• A new section on green building and carbon reduction in the construction industries
• Updating and refreshing Personal Ethics & Sustainability.

You are welcome to download and use this information under our free Creative Commons licence.

Visit our PMKI Library for free access to many more papers and articles: https://mosaicprojects.com.au/PMKI.php

Our paper looking at the scheduling challenges in agile and distributed projects has been published in the February 2003 edition of PM World Journal: https://pmworldjournal.com/

Critical path theory is based on an assumption that to deliver a project successfully there is one best sequence of activities to be completed in a pre-defined way. Consequently, this arrangement of the work can be modelled in a logic network. However, while CPM has proved to be an effective controls tool for many types of projects, it is equally apparent the CPM paradigm does not apply to a wide range of other project types including soft projects and distributed projects.

The focus of this paper is to:

• Briefly define the management assumptions that support the use of CPM scheduling, its origins, and limitations
• Develop a classification framework of project characteristics to help define the potential usefulness of CPM scheduling
• Briefly describe some of the management approaches currently used in non-CPM projects including agile and lean, their benefits and limitations
• Consider the application of the framework discussed above applied to a typical wind farm project
• Develop general recommendations for the management of non-CPM projects focused on optimizing the efficient use of resources.

Based on this foundation, two additional papers will look at:

1. Implementing a robust system for reporting progress and predicting completion in agile and distributed projects that can be applied to any class of project.
2. Assessing delay and disruption in agile and distributed projects where the use of a CPM schedule is not viable.

Download Scheduling Challenges in Agile & Distributed Projects: https://mosaicprojects.com.au/PDF_Papers/P208_Scheduling_Challenges_in_Agile_+_Distributed_Projects.pdf  

For more on this topic see: https://mosaicprojects.com.au/PMKI-SCH-010.php#Issues-A+D

The naming convention 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.

Increasing Normal Decreasing Neutral

An increase in activity B will delay completion, but a reduction has no effect. There are two variations on this type of construct.

A 1-day increase in the duration of activity B will increase the project duration by one day, however, reducing the length of activity B has no effect on the project’s duration.

Increasing Neutral Decreasing Reverse

An increase in activity B has no effect, but a reduction will delay completion. Again, there are two variations on this type of construct.

A 1-day increase in the duration of activity B has no effect on the project’s duration, however, reducing the length of activity B by 1-day will increase the project duration by one day.

Easy CPM, is designed for people who know how to drive scheduling tools and want to lift their skills to the next level. The book is available for preview, purchase (price $35), and immediate download, from:
https://mosaicprojects.com.au/shop-easy-cpm.php  

Our recently uploaded presentation Scheduling Challenges in Horizontally Distributed Projects looks at the challenges of scheduling, managing, and claiming delays in, horizontally distributed projects. The issues in this type of project are similar to the problems encountered in managing project being delivered using an Agile approach using traditional forms of contract. The presentation linked below is the start of a journey, we have a series of in-depth papers planned for 2023 – watch this space. 

Horizontally distributed projects have two dominant characteristics, the majority of the work is comprised of a series of physically separated units that are similar or identical in design, and the logical dependencies between the different units are either non-existent or minimal (think of an off-shore wind farm). In this type of project, most of the components are identical and can be used anywhere, which means the work can be planned in almost any sequence, and that sequence can be easily changed at almost any time. This type of project is not well supported by either traditional CPM scheduling, ‘line of balance’, or other traditional project controls paradigms. The challenge is compounded by the fact that some projects are suited to the underlaying principle in CPM that there is one best way to plan and deliver the works, others (typically distributed and/or agile) have no pre-set requirements for the work sequence and others have some level of mandated logical sequence that affects some parts of the work, but not others.

We suggest the primary consideration in planning and managing a distributed project is optimising resource flows. The consequences of re-sequencing if needed are not based around traditional CPM logic, rather the loss in resource efficiency which is much more difficult to assess and measure. This is particularly true when you need to separate productive efficiencies under the control of the contractor from disruption caused by the re-sequencing.

This initial presentation defines the concept of a horizontally distributed project, and then based on some practical examples, highlights the challenges of assessing delay and disruption based on traditional paradigms of CPM scheduling. It will conclude by offering suggested ways to adapt project controls and contractual requirements to provide a sensible assessment of project delays.

This sets the framework for the papers we have planned for 2023 which will:

1. Generalize the problem and consider the scheduling Challenges in Agile and distributed projects
2. Develop options for predicting completion in Agile and distributed projects drawing on a range of alternatives in both Agile and other methodologies.
3. Consider the challenges faced by tribunals and courts in assessing delays in Agile and distributed projects 

Download the initial presentation from:  https://mosaicprojects.com.au/PMKI-SCH-010.php#Issues-A+D

Project Controls Expo Australia 2022 will run in Melbourne from 29^th to 30^th November and has a packed program totally focused on project controls.  I will be busy on both days:

On the 29^th in the ‘back to basic’s zone’ my session is: EVM – it’s not as hard as you think! This session will look at establishing and operating and running an EVMS, based on Australian Standard AS4817:2019 (the Australian adoption of ISO 21508), using simple tools. The session will briefly cover:
–  Understanding EVM, what it is, and what it is not.
–  Define the key elements and objectives of EVM
–  Demonstrate the creation, and use of EVM on a small bridge project.

 If you cannot make the session most of the information is available from: https://mosaicprojects.com.au/PMKI-SCH-040.php#Overview 

Then on the 30^th I will be looking at a major challenge to traditional CPM and forensic assessment in: Scheduling Challenges in Horizontally Distributed Projects

The challenges of scheduling, managing, and claiming delays in, ‘horizontally distributed projects’ are not well supported by traditional project controls paradigms.

Horizontally distributed projects have two dominant characteristics, the majority of the work is comprised of a series of physically separated units that are similar or identical in design, and the logical dependencies between the different units are either non-existent or minimal (think of an off-shore wind farm).

In this type of project, most of the components are identical and can be used anywhere, which means the work can be planned in almost any sequence, and that sequence can be easily changed at almost any time. This type of project is not well supported by either traditional CPM, or ‘line of balance’ scheduling.

The primary consideration in planning is optimizing resource flows, and the consequences of re-sequencing are not based around traditional CPM logic, rather the loss in resource efficiency which is much more difficult to assess and measure. Particularly when you need to separate productive efficiencies under the control of the contractor from disruption caused by re-sequencing.

This presentation will define the concept of a ‘horizontally distributed project’, and then based on some practical examples, highlight the challenges of assessing delay and disruption based on traditional paradigms of CPM scheduling.  It will conclude by offering suggested ways to adapt project controls and contractual requirements to provide a sensible assessment of project delays. As soon as PGCS is over, finishing the research and writing this presentation is my next challenge.

More to follow on this.

The publication of The Origins and History of Earned Value Management in the August edition of PM World Journal (Vol. XI, Issue VIII) marks the end (almost) of a long journey.

This paper looks at the creation of earned value management (EVM) in the 1960s and its development and evolution through to the 2020s. However, the concept of EVM did not suddenly appear, the foundations of EVM were laid by previous generations, this paper demonstrates EVM is a synthesis of ideas and concepts some of which are hundreds of years old. The four precursors to EVM are the use of computers to calculate time schedules (CPM and PERT), sophisticated engineering cost controls, the use of breakdown structures to aid management, and the emergence of the concept of modern project management.   

The use of computers to analyze project schedules in the late 1950s brought science to the management of time. There was a strong desire in the US Government for similar levels of sophistication to be applied to cost management on defense projects. This was the catalyst for the development of EVM in the early 1960s. The development of scheduling is traced in the papers listed in The History of Scheduling.

The discipline of engineering cost management was well established in the early part of the 20^th century and its roots are much older. The limitation was the process of cost control using paper based manual systems tended to be retrospective. The development of cost engineering is traced in The History Cost Controls.  

The idea of using breakdown structures to define, and then control, work also has a very long history. The Work Breakdown Structure (WBS) is at the heart of EVM. The development of the WBS is described in The Origin of Work Breakdown Structures (WBS). 

Finally, a project controls system needs a defined project to control. The concept of modern project management is relatively new, although again its roots are very deep. Its development is traced in Origins, and trends in, modern project management. 

When these different strands of development were brought together in the USA in the 1960s, EVM emerged. Tracing each of the histories outlined above has been a fascinating journey.  The papers and many of the source materials are freely available to download from the history section of the Mosaic website: https://mosaicprojects.com.au/PMKI-ZSY.php.

The problem with studying history is every time you look at something, there’s other interesting facets to analyze and research. I have identified two areas where I’m likely to go next (but not for a few months):
–  Documenting the early mainframe computer software that was used for CPM, PERT and EVM.
–  In March 2023 Earned Schedule will be 20 years old, its development and the challenges will make an interesting story.

In the meantime download and enjoy The Origins and History of Earned Value Management: https://mosaicprojects.com.au/PDF_Papers/P207_EVM_History.pdf

And…. If you find any errors, or have additional information let me know. I routinely update these papers as new information comes to light. 

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: https://mosaicprojects.com.au/PMKI-SCH-013.php#Process5

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: https://mosaicprojects.com.au/shop-easy-cpm.php