How We Confuse Ourselves
A fair amount of confusion and contradiction permeates among and across the literary works that deal with Project Time Management. Some of this confusion is inherent in the subject matter itself and cannot be avoided. But much of the confusion is entirely avoidable.
However, Confusion Avoidance requires both Will and Influence on the part of those who have a vested interest and recognized voice in precisely how Project Time Management is implemented on a given project Let’s take them separately:
- Will: Avoiding confusion requires the will to act — one’s conscious, purposeful, deliberate, and steadfast desire to do so. It requires a level of diligence and mental focus that can at times become tiring, fatiguing, and overwhelming. It is not an assignment for the faint of heart.
- Influence: On the other hand, influence refers to one’s standing in the broader Project Time Management community. It is not enough to want, or even have a great idea about how, to avoid confusion, for there to be a meaningful and lasting effect. The catalyst for change must have broad influence.
Change of all kinds, which afflict all projects, come from only two places: externally and internally.
- External Sources of Change: External sources of change tend to be more formal, more disruptive, and less respectful of any preconceived, agreed-upon Project Time Management approach. Included within the External class of changes that can affect a single project are government regulations, contracts and other owner mandates. It also includes “best practices” and standards that are imposed by industry groups striving to standardize approaches to Project Management. [To their credit, these institutions recognize the inherent struggle to balance multi-project standardization (even across disparate industries) with the need for project-level autonomy.]
- Internal Sources of Change: Factors within this class of change evolve out of the Project Execution process itself. Just as rough or calm seas are merely changing states of a consistently-present ocean beneath the ship, within this class of change is the ever-modulating state of operational conditions that constitutes the platform upon which the Project is built. In Construction there are many such commonly encountered changes: to name just a few; shifting weather patterns, subsurface ground conditions, the unpredictability and uncertainty of workforce availability, quality, or performance; the timely arrival to site of critical materials; the quality and timeliness of essential information; and so forth.
It should be obvious that our greatest opportunity to influence the elimination of confusion on projects rests mainly in the External Change realm. For it is here that decisions are made that directly affect how projects are, can be, and (quite often) must be managed. Both explicitly through edict, and implicitly through accepted, recommended, or adopted practices, those with sufficient Influence are forever invoking and forcing change. And whether they realize it or not — or intend it or not — their decisions can (and often do) easily and innocently confound otherwise straight-forward understandings.
To make my point, let me give an example. In this case, a recommended or accepted practice undercuts a previously well-functioning and readily understood concept: Earliest Dates. For the sake of those possibly unfamiliar with the term, Earliest Dates (Earliest Start and Earliest Finish) indicate the earliest possible time that an Activity in a schedule can conceivably start or finish, given prior logic, activities, and durations as depicted in the CPM schedule’s interwoven network of activities.
Confusion Example #1: Earliest Dates
In this example, we will consider how the rules (formula) for determining an activity’s Earliest Start have gradually changed over time — to the extent that now the word “earliest” no longer means “earliest.” Helpful to this discussion will be a simple two-activity logic diagram, as introduced in Figure 001.
Figure 1: Truly Earliest Start Interpretation
This figure presents us with a lot of important and valuable information.
- We see that there are two activities: Washing Dishes and Drying Dishes.
- We can assume that there are at least two individuals involved, since one person could not be performing both dish-washing and dish-drying at the same time.
- We see that it is either ten o-clock, or that the “work” is triggered to commence at ten o’clock, and no earlier, as denoted by the Start-No-Earlier-Than (SNET) designation.
- We see that the washing of the dishes will require fifteen minutes, and included among the dirty items in the sink are some “pots with stubborn baked-on grease.”
- We see that the drying of the dishes, if performed without interruption, is estimated to need seven minutes to accomplish.
- We see that, for whatever the reasons, the dish-drying activity is called to start after two minutes of dish-washing have been performed. Hence, we estimate Dry Dishes will commence at 10:02.
- We see that, if the Dry Dishes activity commence at 10:02, as shown, it will not be able to work uninterrupted for the balance of its duration, because the Wash Dishes activity is moving at a much slower pace. The person drying the dishes can expect to be standing idle longer than he/she will be actually drying dishes!
- We see from the red arrows and accompanying notation that the Dry Dishes activity enjoys seven minutes of discrete Total Float (up and above any other Total Float it might have thanks to prior and subsequent logic surrounding the activity).
In terms of interpretation and usage, the Project Manager for the ”project” that this “schedule” represents has all the information that she needs to make decisions about how to execute this work. In one extreme, she can call for the Dish Dryer to be ready to commence at 10:02 (as shown). At the other extreme, she can maximize Dish Dryer efficiency by postponing the Dish Drying activity until 10:09. The take-away, from this paragraph, is that the Project Manager has several options, and the schedule, as shown in Figure 001, provides a lot of useful information upon which to make informed decisions.
Now let’s look at Figure 002, in which we see the same two activities. But this time we are exposed to a scheduling technique used in the Critical Path Method called “Continuous Durations” or “Contiguous Durations.” I first encountered this option in P3 (Primavera Project Planner) back in the late 1990s, where a scheduler was given the option of choosing a toggle setting of either “Contiguous or Interruptible Durations.” If I chose Interruptible, the result was what we just studied in Figure 001. But if I chose Contiguous, the result was as shown in Figure 002.
Figure 2: Delayed Earliest Start
Let’s look at Figure 002. The first thing we notice, jumping out at us from the bar chart on the right, is that the Dry Dishes activity is now one solid, constant block of work. We see that it starts at 10:09, and proceeds without interruption to 10:16.
You should be aware of how P3 calculates the Earliest Start of 10:09, for such awareness gets to the point of this example, and this blog article. P3 essentially violates the decades-old understanding of a Forward Pass, and instead calculates backwards in order to determine the Earliest Start.
- First, P3 determines the Earliest Finish for Dry Dishes, by honoring the Finish-to-Finish tie of one minute. Since Wash Dishes cannot finish any earlier than 10:15, then Dry Dishes cannot finish any earlier than 10:16.
- Next, P3 subtracts the activity duration for Dry Dishes, which is seven minutes, and arrives at an Earliest Start of 10:09.
But there is just one small problems: 10:09 is not the earliest that Dish Drying can start!! Keep in mind that for the entire life of P3, which spans more than two decades, Primavera offered the scheduler the option to choose between Contiguous or Interruptible. And in the early years, Interruptible was the default.
But somewhere along the way, Contiguous became the default setting. P3 maintained the option to change the setting, and most seasoned schedulers would do just that. But the default setting prevailed in schedules where the scheduler was not aware of the setting. Over time, the prevalence of Contiguous Durations in schedules was rampant.
Today, in P6, there is no option for Interruptible (to my knowledge). As a result, what P6 calls the Early Start (10:02) is not, in truth, the earliest that it could start if the artificial restriction imposed by the software setting wasn’t calling the shots.
Finally, just in case you are thinking that I am merely making a well-presented argument for what is essentially a technical point of no real-world importance, consider the loss of those precious seven days of Total Float. In Figure 001, we saw that the Dish Dryer knew that he or she had a period of thirteen minutes (10:02 through 10:15) to perform six minutes of Dish Drying. Just where those seven minutes of Total Float would occur was left to the “Project Team” (in this case the Dish Dryer and Dish Washer) to decide.
Defenders of Contiguous Durations insist that there is really no downside or negative effect to its practice, but I disagree. First, from a practical perspective I don’t happen to believe that scheduling software should have greater influence over how a project is executed than the Project Manager does. Second, any time we squander precious Total Float we endanger the project.
Let’s expand our example one last time. Let’s look into that sink of dirty dish water and see what needs to be washed. As already noted there are several pots with stubborn baked-in drips. The Dish Washer will leave these time-consuming items for last. But, other than four such pots, the remainder of the sink’s contents is comprised of dishes and silverware, each piece of which should be easy to quickly wash.
Now let us suppose that among the dishes are two ornate serving platters that the Dessert Chef is waiting on, in order to prepare a dessert for a party of six who are just about finished with their entrées in the dining room. Suppose that this urgency is communicated to the Dish Washer, who makes a point of washing those two platters in the first minute of the Wash Dishes activity.
The Dish Dryer is not scheduled to start until the end of the second minute, which is intentional: it allows the majority of water runoff to drain from the platters, so that the Dryer’s towel doesn’t get sopping wet after only a few dishes. By extension, we can see that the Dish Dryer will have dried the important platters within the first minute of his work.
Figure 3: Contrasting Interruptible and Contiguous Durations
All of this is shown in Figure 003, left side, where we see that the Dessert Chef should have the needed platters by 10:03. The Dessert Preparation activity has an eight-minute duration, and from what we see in the logic on the left, the desserts should hit the awaiting diners at 10:11.
But now look what happens if we are using a Contiguous Duration setting, with its delayed “Earliest” Start. Since Dish Drying is not allowed to start until 10:09, then those needed platters are not available to the Dessert Chef until 10:10, and the desserts will not arrive to the diners before 10:18. Notice that the difference between the two dessert arrival times (10:11 and 10:18) is the same seven minutes of Total Float that we enjoyed with traditional Interruptible Durations, but that had been squandered under the Contiguous Duration approach.
Folks, while the above discussion may have opened your eyes to what are clearly deficiencies in the current (Contiguous Duration) practice, the main point I am trying to make is that, from an institutional level, an External Change has been imposed on the Project Time Management world that fundamentally redefines the word “earliest.”
I would suggest that a more appropriate term might be Preferred Start. Why do I say this? Because the underlying rationale for using Contiguous Durations in the first place is to facilitate greater efficiency in the performance of the restricted activity. It traces to a well-accepted truism that uninterrupted work is far more efficient than stand-around work.
But this is a management decision, is it not? The Contiguous Duration approach favors efficiency, which in its greatest consequence, improves project economics. But the Interruptible Duration favors the project’s temporal interests. In our example, it does this in two ways. First, it supports the earliest possible delivery of desserts to the customers. Second, it holds onto Total Float for subsequent, downstream Dish Drying activities.
This second point deserves a further brief discussion. When work, any work, is performed without Total Float, it is like working without a net! There is no allowance for anything to go wrong. Suppose the Dish Dryer accidentally drops the towel into the sink of dirty dish water, and that fresh towels are downstairs in the laundry room. Or suppose the Dish Dryer accidently cuts his hand on a knife and needs to take a few minutes to contain the bleeding and bandage the wound, before returning to duty.
In the Interruptible Duration scenario there would be ample Total Float to absorb either ”incident.” But in the Contiguous Duration scenario, there would be no Total Float. And so, if we assume that either incident would delay Dish Drying by three minutes, then dish (under the Contiguous Duration setting) drying will not finish until 10:19. It would be a one-for-one delay to the end of Dish Drying, because there would be no Total Float available to absorb unexpected “surprises.”
Software Settings for Durations Just one Example
The above example of the effects of two alternative software settings for determining Earliest Dates is just one example of how External Influences can alter the meaning of concepts that were previous understood, rational, and effective. Sadly, there are many, many others similar instances of policies affecting what had been common sense understandings. Which examples can you think of? Leave your comment below?
This blog is long enough, so I won’t go into other examples. Suffice it to say that the broadly-accepted objectives and goals of Project Time Management as a discipline might be better served if those with the greatest Influence were to be as diligent as possible when checking that new approaches and innovations do not unintentionally undermine, contradict, or even reverse well-established understandings.