Why Won’t We Recognize the Value/Cost of Time on Projects?

A few weeks ago, I engaged in an Internet discussion with a very knowledgeable project management thought leader. Make no mistake – this is someone for whom I have a great deal of respect. But when the topic of the cost of time on projects came up, he was dismissive, stating that the value of early completion on most of the projects on which he consults is very small or non-existent.

Let’s think about this: for several years, he has been residing overseas and consulting on projects many thousands of miles from his home. And his consulting fee is definitely not cheap! How important would a project (or program, or portfolio) have to be in order to justify the fees of such a consultant? How large its budget? How great the expected value of the investment?

One of the fundamental aspects of any type of investment is that the length of time to “maturity” is a key variable. The return/benefit that any smart investor will demand is always based in part on how long the wait for that return is likely to be. (There’s an old Bajan saying: “Wait is a heavy load!”) The longer the wait, and the more money that will be “tied up” in that investment, the higher the rate of return that the investor will demand as justification for the project/investment.

One thing of which you may be sure: organizations do not engage expensive overseas consultants to work fulltime on a project with a million dollar budget. Whatever the projects/programs on which this consultant has been working, the budgets are almost certainly over $10 million, and likely over $50 million.

Let’s take conservative numbers: even at just 3% interest, the cost of tying up $10 million is $300,000 per year. That’s $25,000 per month. For a $50 million project, that would be $125,000 per month.

And that does not include:

  1. The opportunity cost of not having that money to invest elsewhere sooner.

  2. The risk of taking longer than planned, a risk that is retired immediately if the project finishes early. Almost everyone would agree that there is a significant cost to finishing most projects late. How much is it worth to eliminate that particular risk?

  3. The “marching army” costs of overhead and level-of-effort activities to support the project. These costs often add up to 10% – 20% of the total cost of a large project. These are costs that continue, week after week, until the project ends. Finishing earlier usually truncates these costs.

  4. The very large reduction in value if the project in question happens to be an enabler project. This is a topic I cover extensively in my book Managing Projects as Investments: Earned Value to Business Value. A delay on an enabler project means a postponement in the value delivery on all the other projects that it is enabling. For example, inkjet printers are often sold at break even or less – their profit comes from the ink cartridges whose sale they enable. Delay printer production and you delay cartridge revenues.

  5. The loss of flexibility that a shorter schedule would allow. Blake Sedore pointed this out to me in conversation: a shorter schedule can sometimes have value not so much by finishing earlier but by allowing the project (or manufacturing process) to start later! This delays committing to a specific strategy and maintains flexibility – perhaps the extra time will allow for better targeting of product scope, or even permit cancelling the project if a sudden change in market conditions makes it no longer a sound investment. (I plan to discuss this interesting idea further in an upcoming blog article.)

(I make no pretense that the above list includes every possible benefit that a shorter schedule would bring — but it’s a start! If you have any additional benefits to a shorter project schedule, please go to this discussion thread in the FORUM and list some of them. perhaps together we can create a useful checklist.)

So why did this very competent consultant not recognize the value of a shortened project duration? It’s simple – he wasn’t looking for it. The PMBOK Guide ® does not discuss the value of project acceleration. The vast majority of project management software provides no field that allows the user to enter a value/cost of time, either acceleration or delay. (And that omission combines with the almost universal failure of software to compute critical path drag to prevent the crucial calculation of the drag cost of critical path activities, a data item that can justify added resources.)

So is it possible, however unlikely, that on the consultant’s specific projects there was no value to the sponsor/customer of an earlier finish? Absolutely! There are indeed projects where there is no advantage to a shorter schedule. There are even projects where finishing earlier has a negative impact on the project investment! (This is particularly true if a project is not on the critical path of the program of which it is a part. For example, early completion of a satellite to be launched on a rocket does nothing to shorten the program if the critical path goes through the preparation of the rocket. The satellite project would have no drag on the program’s critical path, so that finishing it early would only increase its program float, as well as perhaps require additional storage.)

However, such projects are so unusual that it becomes all the more important to clearly identify these exceptions to the rule. It is critical to perform the necessary cost/benefit analysis for earlier completion, taking into account all of the issues I’ve mentioned above, and more. If after all that analysis there really is no advantage (or perhaps a disadvantage) to the sponsor/customer from an earlier completion, that fact should be made known to key team members: “This is one of those rare instances where we won’t be looking to shorten the project!”

But the rule should always be to analyze and quantify the value/cost of time and, if there is a contract involved and value to early delivery, to seek a win-win arrangement: an early completion incentive to the contractor based on a portion of the value to the customer of such a happy result.

Have a great weekend!

Fraternally in project management,

Steve the Bajan

Blake Sedore Blog on Drag Cost: Applying Critical Path Drag in Manufacturing

The first-ever Guest Blog is now up at the Total Project Control website, available for reading and discussion. It is by Blake Sedore, the manufacturing engineer whose recently published MIT thesis on using critical path drag analysis to accelerate semiconductor production and increase throughput has received a ton of attention. You can click on the Guest Blog here, and also make comments or ask questions of Mr. Sedore in the discussion FORUM on this site.

In this Guest Blog, Mr. Sedore explores the experience both for himself and his customer of recognizing the opportunities for improvement pointed about by the drag analysis:

“The results of my project were quite eye opening, both for me and for my client, and I believe that this effort shows that the critical path method and critical path drag have a strong application to the manufacturing industry.”

And he goes on to write:

“I have come to realize that the analysis has the potential to go much further. MUCH FURTHER. The analysis does not end with calculating the critical path drag – this is actually just the beginning. The drag is merely a stepping stone to get to drag cost, which is the metric that truly matters, as it allows you to determine the impact that the drag of a critical path item has on the bottom line.”

And he goes on to discuss how the drag cost savings opportunity offered by reducing Work in Progress:

“And in manufacturing, when you repeat the process again, and again, and again, and again, and again…that drag cost is going to add up. BIG TIME.”

Mr. Sedore’s thesis article  “Assembly lead time reduction in a semiconductor capital equipment plant through constraint based scheduling” can be downloaded from the MIT website here.

Read his entire Guest Blog and post questions for him in the FORUM thread.

Fraternally in project management,

Steve the Bajan

June Issue of PMI’s PM Network Magazine: Great Review of Managing Projects as Investments

Earlier today I decided to Google the title of my book Managing Projects as Investments: Earned Value to Business Value. I was delighted to discover that Gary Heerkens has written a great review of it in the June issue of PM Network in his “The Business of Projects” column.

PM Network June cover

In my previous blog article, I summarized a series of previous articles on critical path drag in the following way:

Critical path drag is not, in my opinion, the most valuable innovation that I have included in my books Managing Projects as Investments and Total Project Control. I think the focus in those books on defining and planning projects as investments and then tracking them in scope/cost/schedule integrated fashion through the DIPP and the DPI indexes is what can take project management, and the project manager role, to the next level of professionalism.”

So I am delighted that Mr. Heerkens’s review is so positive despite not even mentioning critical path drag! One paragraph from his article reads:

“Mr. Devaux’s strong points from his book clearly show that there is a wide variety of ways that sound, business-based decision-making can be brought to bear on the way we manage project implementations. One of the many insightful passages that truly captures the spirit of the book is this: Even though their final value might not be revealed for a long time after the initial investment is made, projects should always be managed in such a way as to maximize their expected return.”

But read the whole article. The Google link locates it here. Or if you receive PM Network magazine in the mail, it’s on page 70.

And if you have any comments or questions, please click here to go to the thread in the Discussion Forum.

Fraternally in project management,

Steve the Bajan

How to Make Critical Path Drag a Standard Scheduling Metric?

Okay, so I’m asking.

And this question and article are timed to inaugurate the new discussion forum part of this site, where readers can now go to:

  • Respond to discussion topics like this one and others I will be launching, and
  • Start their own threads to discuss Total Project Control techniques and/or other project management (or other!) topics that are of interest.

Just click on the FORUM tab, and please keep all discussions respectful and courteous. Now back to the point of this blog, to which you can then post your reactions in the Discussion Forum.


Critical path drag is not, in my opinion, the most valuable innovation that I have included in my books Managing Projects as Investments and Total Project Control. I think the focus in those books on defining and planning projects as investments and then tracking them in scope/cost/schedule integrated fashion through the DIPP and the DPI indexes is what can take project management, and the project manager role, to the next level of professionalism. But critical path drag is the metric and technique whose value is the most obvious and whose omission from critical path analysis is the most glaring! Why no one previously “discovered” it and its implications, or figured out how to calculate it, is a complete mystery to me. (A student of mine once remarked that I see things that are glaringly obvious!) Yet, 16 years after the first edition of Total Project Control was published, the metric is still not in the PMBOK Guide ® and only one PM software package (Spider Project) currently computes it. In the past two or three weeks, I have published a number of articles on drag and drag cost. Here are a bunch of them if you want to read them again, all gathered together under the “drag” tag. If you haven’t read them yet, you might want to go from bottom to top, in the order in which I wrote them. I honestly believe that anyone who understands critical path analysis will immediately appreciate the value of this new metric:

  1. Unlike the non-critical metrics total float and free float (which every PM software package computes and which are undoubtedly a part of every PMP exam), drag is critical! Why on earth do we quantify the non-critical stuff but not the critical?
  2. Unlike float, drag is always costing our project time and almost always costing it money, in both the form of reduced expected value and in the form of increased overhead through indirect costs. Why wouldn’t we want to compute these costs so that perhaps we can reduce them?
  3. Drag cost is a crucial metric for justifying resources. The true cost of a critical path activity is the sum of its resource costs plus its drag cost. Shouldn’t we want to measure this so that we might be able to lower the true cost by increasing resource costs but thus reducing drag costs by even more?
  4. As every project is an investment, all project work should be adding more value than it costs. We should therefore want to ensure (by combining the value breakdown structure with true cost) that no optional work is included on the critical path whose value-added is less than its true cost. (Here are some blog articles with VBS tags.)
  5. Project managers often have trouble generating an initial schedule that will meet the date target the sponsor/customer has specified. On a large project, drag computation is a crucial metric for seeing opportunities for schedule compression.
  6. Even if we start the project with enough time, what happens when the schedule slips? Every experienced project manager knows that feeling of searching for opportunities for schedule recovery. Again, critical path drag is the crucial metric for seeing the opportunities to iteratively pull in one critical path, then another, and yet another until an acceptable schedule has been achieved.

So I ask the readers of this blog: having published lots of books and articles about drag, having presented many PMI webinars and chapter dinner presentations, what should I do to get this information out into the wider PM world and to spur software companies to start measuring this critical metric that’s always there and costing time and money (and maybe human lives!) whether their software deigns to measure it or not? Fraternally in project management, Steve the Bajan

Answers to the May 22 Weekend Puzzler on Drag Cost

My recent Weekend Puzzler blog, to calculate drag and drag cost (in human lives) attracted quite a bit of attention. A total of 241 different readers viewed it over the weekend, generating a total of 288 views and pushing the total for the blog thus far this year to just over 6,900. This is sufficient encouragement to make me believe that there is a readership for relatively complex project management information, and therefore to keep doing this. This is despite the fact that only 5 people entered a total of 16 answers in the “poll” multiple choice selection format. Oh, well, perhaps many other people figured out their answers but just didn’t enter them into the poll. Of the 16 answers entered into the poll, 10 were correct (and I have a sneaking feeling that one person got them ALL correct, in which case congratulations to that person!). First, from the last article, the final network diagram schedule with all the schedule computations on which the drag cost questions were based: Fig 4 All FS network lives for blog Now here are the answers and explanations. *****

  1. If Activity B takes 10D longer than planned, how many more lives will it cost? A= 7 B= 10 C=26 D=40 E=50 (4 correct answers out of 5)

If Activity B takes 10D longer than planned, it will take 15D, use up all 8D of its float, and migrate to the critical path with 2D of drag. Those 2D will push the project duration to 69D and cost 2 * 5 lives, or 10 more lives lost.

  1. If we can shorten Activity D to 3D instead of 7D, how many more lives would that save? A= 0 B= 7 C=10 D=14 E=20 (1 correct answer out of 3)

If Activity D is shortened to 3D instead of 7D, the first 2D will be its drag and the next 2D will increase its float to 2D. Those first 2D will pull the project duration in to 65D and save 2 * 5 lives, or 10 more lives saved.

  1. If we take resources away from Activity P so that it takes 30D instead of 15D, how many more lives will it cost? A= 0 B= 5 C=10 D=12 E=75 (2 correct answers out of 3)

If Activity P’s duration is increased to 30D instead of 15D, that will be an increase of 15D. But P had float of 17D. Therefore the increase in P’s duration will only reduce its float to 2D and will not impact the critical path and the project duration. There will be no change in the number of lives saved/lost.

  1. If Activity P is now scheduled to take those 30D, AND we also shorten Activity K to 12D, how many more lives would it save OR cost? A= 0 B= 7 more lost C=10 more lost D=10 more saved E=50 more saved (2 correct answers out of 3)

With Activity P now having just 2D of float, it means that K’s drag has been reduced to 2D. Now if K is shortened by 10D, the first 2D will be drag and the next 8D will be float. Those first 2D will pull the project duration in to 65D and save 2 * 5 lives, or 10 more lives saved.

  1. With Activity K now planned to take 12D, if we now decide to give some resources back to Activity P so that it only takes 20D, how many more lives would be saved than in Question 4? A= 0 B=10 C=16 D=22 E=40 (1 correct answer out of 2)

With K now having 8D of float, Activity P is on the critical path with 8D of drag. If P is now reduced by 10D, the first 8D will be its drag and the next 2D will increase its float to 2D. The critical path will have changed and now will again go through Activities K and Q. This will also pull the project duration in by 8D, from 65D to 57D, and save 2 lives for each day or a total of 8 * 2 lives, or 16 more lives saved. ****** If you understand this whole process but find drag and drag cost difficult to compute, then please push the powers that be (i.e., PMI, IPMA, APM and all the software companies) to start incorporating these data in their critical path analysis computations. Because the calculations are dead easy for a computer, and this information is critical! Fraternally in project management, Steve the Bajan

Weekend Puzzler: Computing Critical Path Drag on a Project to Save Lives

There has been a lot of discussion of critical path drag and drag cost recently, both in this blog and elsewhere. Most salient was Blake Sedore’s MIT paper about using critical path drag to optimize manufacturing throughput, but there was also this very nice out-of-the-blue comment on LinkedIn, and a number of email conversations. Maybe the importance of these concepts is finally trickling into general awareness.

So with the weekend here (a long one in the US!), I decided it was time to provide another “Weekend Puzzler” of practice in computing drag and drag cost. So I’ve drawn a network diagram below, with all the dependencies finish-to-start (FS), just to make sure it isn’t too complicated. And if there is any step you feel is too complicated or tedious (perhaps like the forward and backward passes), just jump over it to the next diagram, which will have the answers.

To emphasize the importance of these computations, I’ve chosen a project that is intended to save lives: an immunization program, hospital construction, or medical device development, perhaps. But the calculations would be the same if the only benefits were monetary.

After the fourth diagram, there are some additional questions, with the “poll” function making it a multiple choice quiz. I’ll provide the answers and explain them on Tuesday.

And by the way, next week should be interesting in any case. I am hoping to launch a discussion forum, where readers can raise topics they want to discuss, or make general comments. Additionally, I believe the June issue of PMI’s PM Network magazine will become available on-line, and I have reason to believe there may be a very interesting article in this issue.

Have a great weekend, and the Puzzler is directly below.

Fraternally in project management,

Steve the Bajan

Weekend Puzzler

A.  Compute the forward and backward passes for early and late dates, identify the critical path and compute total float.

Fig 1 All FS network lives for blog

B.  These are the answers to A. Now compute the drags of the critical path activities.

Fig 2 All FS network lives for blog

C.  These are the answers to B. Now compute the drag cost in lives not saved for each of the critical path activities.

Fig 3 All FS network lives for blog

D.  These are the answers to C. Use them to answer the multiple choice questions in the “poll”.

Fig 4 All FS network lives for blog

What’s Costing Time? CPM vs. Critical Path Analysis

The most recent article on this blog, regarding the MIT paper about using critical path drag to optimize manufacturing throughput, generated a number of interesting reactions. First, it has been very popular, attracting well over 100 views per day and several “Likes” in the LinkedIn discussion forums where I mentioned it. However, some people seem to have negative views about the value of such a process. All these people seem to be conflating critical path analysis and CPM and they specifically reject CPM as a worthwhile scheduling technique, expressing a preference for critical chain scheduling or one of the flavors of agile methodologies.

So let me try to improve my communication technique: there is an important difference between CPM and critical path analysis!

  • The former is a technique for developing a schedule for a project, and is almost always performed upfront.
  • The latter is a technique to analyze the detailed aspects of any process (like manufacturing), project or program, upfront, during progress, or after completion, with the purpose of identifying, measuring and perhaps reducing the total duration of execution.

Why should we want to reduce the duration of a process or project? Because, to paraphrase what a really smart guy wrote over 260 years ago: “Time is a whole lot of benjamins!” If we start recognizing that all projects and programs are, as my book emphasizes, investments, then we will quickly conclude that two major factors that impact project investment value are:

  • Scope; and
  • Total duration.

Along with that important but often over-emphasized third constraint of cost, these are the parameters over which project teams have some control, and that project and program managers are paid to manage. And we control completion date through the critical path – of any process, project or program!

Whether a project is scheduled using “naked” CPM or resource leveling or critical chain or agile or darts at a dartboard, at the end it still will have an “as-built” longest path (comprised of activities, constraints, sprints, stumbles, dropped batons, feeding buffers, schedule reserve, hesitations, and any other delays) that always determines its total length. Surely if time has value (as it does on 99% or more of projects!), then it must be worthwhile analyzing:

  1. What items are extending the duration (i.e., have critical path drag)?

  2. By how much?

  3. How much is that extension reducing investment value?

  4. What might we be able to do to reduce that negative impact?

traffic jam

It doesn’t matter what method of scheduling we used! Even a serial string of sprints, if analyzed, will usually reveal a place where we can shorten the critical path by adding a resource, or dividing the process into parallel streams, or deciding not to include functionality whose value-added is worth less than the time it consumes (i.e., its drag cost). And if someone says that doesn’t happen, how do they know unless they do the analysis and determine which sprints/activities/resources/rework have how much critical path drag?

If some item that you need to perform your project is really expensive, wouldn’t you try to see if you could get it for less? Well, how is that any different from using critical path analysis to identify the big drag cost items and seeing if you can perform them for less?

That is part of the beauty of Blake Sedore’s analysis for his MIT Master’s thesis. It’s entirely possible that the manufacturing organization was comfortable with their process, and felt that it was optimized. Then he performed the critical path analysis, identified where the drag was, figured out how to reduce it, and voila! – throughput and value were increased!

Whatever the scheduling method, critical path analysis has always had value. I remember reading an article over 20 years ago about how Motorola used it to increase throughput on the shop floor of their pager division. But the enhancement of critical path drag computation puts the emphasis where it belongs: not on what can take longer without causing delays (i.e., float), but on what’s causing how much delay. The technique for computing it is straightforward, if somewhat brain-intensive in a complex process or project.

A process that is both brain-intensive and can add a lot of value – gee, that sounds like just the sort of thing software packages should compute!

Fraternally in project management,

Steve the Bajan

New MIT Paper: Using Critical Path Drag to Optimize Manufacturing Throughput

Eureka! Through the wonders of Google, I have just discovered a new paper describing the practical application of the critical path drag metric to optimize a manufacturing process. The paper is by Blake Sedore and the paper was his thesis for his Master’s of Engineering degree in Manufacturing. It’s titled: “Assembly lead time reduction in a semiconductor capital equipment plant through constraint based scheduling.” You can find the abstract through the Massachusetts Institute of Technology website at the URL below. You can download the complete PDF file by clicking on the download link at the end of the abstract.


Manufacturing semiconductors

As far as I know, this is the first time that someone other than yours truly has analyzed a manufacturing process using this metric, and certainly the first time someone has written a paper about it. The paper is 83 pages long and, by my count, mentions drag about 37 times.

From the abstract:

“A preliminary build schedule was developed that prioritized critical path procedures. A trial of this build schedule achieved an assembly lead time of 39 hours, resulting in a 70% reduction from the current average of 5.5 days. This trial was also accomplished with 76% of the average labor hours for assembly. A production build schedule with a lead time of 43 hours was developed based on the trial results. This schedule allows for production rates of up to 5 machines per week to be achieved with the current shift structure of the company, without the incurrence of overtime. A critical path drag analysis identified critical procedures with the highest potential for lead time reduction. The highest drag of a critical path item was 260 minutes, accounting for 10% of the assembly lead time.”

In the paper, Mr. Sedore then goes on to describe how he analyzed the possible ways of reducing the drag and made recommendations based on considerations of greatest drag reduction, lowest cost of additional resources, and shortest disruption of the manufacturing process. This last item seems to me to be a new enhancement in the application of critical path drag analysis specific to the manufacturing industry, and I am very excited about it!

I contacted Mr. Sedore and asked him about his experience calculating drag “manually”, as the critical path software he was using (MS Project), like most, doesn’t perform the calculation. He said that it gave him some trouble until he laid it out in Gantt chart form, when the drags on the critical path became more obvious. He also agreed that it would be so much easier if only the software would compute it!

A Gantt chart is usable on a manufacturing project which is likely to consist of no more than a couple hundred steps. But for a project with over a thousand activities, I have found network logic diagrams (aka PERT charts) to be necessary (provided I am not using Spider Project which computes drag automatically). But it’s certainly high time that MSP, Primavera, MicroPlanner, Asta, Safron and all the others started including this functionality. (They will eventually – but when?)

Seeing drag analysis being used by engineers at the most prestigious engineering university in North America is extremely exciting to me! Yes, it should be used by all project and program managers – but it also should be standard usage for analyzing and optimizing circuit board design, software algorithm optimization, disaster emergency response: any procedure with integral steps. Maybe Mr. Sedore’s article will kickstart its usage in manufacturing.

I have invited Mr. Sedore to write a short guest blog for this website about his experiences in using drag analysis. I hope he will do so some time in the next few weeks.

Fraternally in project management,

Steve the Bajan

Multiproject Resource Leveling – Some Advanced Considerations

Yesterday I watched this short (2:45) video by Jennifer Bridges on the important topic of multiproject resource scheduling. I absolutely recommend it for an audience learning the basics, as it’s a good primer on the topic, with some important reminders.

However, one can only say so much in any short video. So in keeping with the general approach of this blog, I thought I would add some considerations that more sophisticated project management professionals should keep in mind. All of these (and more) are explored in depth in my book Managing Projects as Investments: Earned Value to Business Value – but I thought a quick thumbnail list might be of interest.

  1. Always optimize CPM schedules (using critical path drag and drag cost) before you plug them into the resource library and start automated resource leveling. Why? Because the software’s resource leveling algorithm resolves bottlenecks by delaying activities, never by pulling them earlier. Take as an example the case where a resource is only available the first week of each month. If your CPM schedule has that activity scheduled for the second week in April, it will slip to the first week in May. However, if your schedule optimization process had pulled it in to the last week in March, the resource-limited leveling algorithm would schedule it for the first week in April, shortening that path by a whole month. If that path is the critical path, how much is gaining a month worth? And all without increasing the budget by even a dollar.

  2. A shorter schedule is not necessarily a better schedule. What is the value/cost of time on your project? If you know that, you can justify the cost of resources when they are profitable and refuse them when they are not.

  3. Just because Project X has a bigger budget, or greater expected value, or even is managed by the CEO’s brother-in-law, does not mean it is the one that should get an over-allocated resource. The determining factors should be:

  • The amount of time that not getting the resource when it’s needed will cost in total across all the competing projects; and
  • The value/cost of that time on each project.

These factors must be quantified (i.e., monetized) and the decisions made on the basis of greatest benefit to the overall organization.

  1. The amount of time that a project is delayed due to resource bottlenecks is, in Total Project Control terms, called resource availability drag (RAD), i.e., the project delay caused by insufficient resources. But the value lost through such delay is called the cost of leveling with unresolved bottlenecks (the CLUB). That dollar value, if known to the project manager, can be used to justify targeting the needed resource to their own project.

  2. The CLUB for a particular resource, on all projects over a period of time (a quarter, a year) can add up pretty quickly. Organizations are not tracking this vital metric for “rightsizing” an organization’s staffing levels. This is a crucial function that a good PMO can serve, greatly justifying its existence for the next time the “costcutters” want to get rid of it.

  3. Finally, remember that the resource-leveling algorithms in project management software packages can vary greatly in terms of functionality and robustness. Some automated resource leveling algorithms are woefully inadequate, adding time needlessly to a project schedule. A good project manager can often improve the post-leveling schedule by eyeballing it and making intelligent decisions.

I explore this subject much more thoroughly in my two books.

Fraternally in project management,

Steve the Bajan

Excellent article on avoiding the use of negative lags

Emily Foster of Ten Six Consulting often writes excellent project management articles. The new one is titled The Negatives of Negative Lag. It explores the risks involved in using negative lags (aka “leads”).

One little addition is to note that in positive lags on SS (and SF) relationships, the lag almost always represents what Spider Project would refer to as a “volume” lag, which represents work/time that is already modeled in the predecessor, i.e., digging the first 25m. of trench. If it is on the CP, the drag and drag cost would then be in the predecessor activity, pointing the scheduler to the fact that to shorten the project, we need to get that first section of trench dug faster. (BTW, a lead, being negative time, has no drag.)

There are often good articles at the Ten Six Consulting site. I find it a useful bookmark.

Fraternally in project management,

Steve the Bajan