Precedence Networks - Construction Project Scheduling and Control - page 118

project's completion date. We just proved this when we compared Figures 5.24
and 5.25. Maybe the project manager does not need to discuss the types of
float with his or her work crews, but he or she must understand—in layper-
son's terms—that some activities must start with a certain portion (but not
all) of them finished before a succeeding activity can start. Failure to under-
stand this point may result in an inaccurate schedule and a possible conflict
between field operations and the office-prepared schedule.
2. In reality, most project managers and schedulers overlook the issue of inter-
ruptible or contiguous activities and may also overlook the type of relationship
and lags. They try to compensate for the inaccurate logic by “correcting” it
through schedule updates. For example, the baseline schedule may show a
Clear & Grub activity with 12 days' duration followed by an Excavation activ-
ity (FS relationship). Once the project starts, you may indicate an Actual Start
for Excavation only 4 days after Clear & Grub had started, a clear violation of
the set logic. The scheduling report may indicate “Activity started; predecessor
has not finished.” The calculation of the updated schedule will depend on
whether you want to apply Retained Logic (i.e., schedule the remainder of
Excavation after the predecessor, Clear & Grub, has finished) or to apply
Progress Override by allowing Excavation to continue independently of the
Clear & Grub activity (this topic is explained in more detail in chapter 7).
This option is available with some computer software programs, but the
author's observation has been that many software users never pay attention
to this choice. As a result, the program always uses the more conservative
assumption—Retained Logic—which may result in a later calculated finish date
for the project.
3. At the same time, the scheduler should use the KISS (keep it simple and smart,
not stupid) approach as much as possible. Sometimes, instead of having a com-
bination (SS and FF) relationship with lags, splitting the predecessor activity
into two activities and then using the traditional FS relationship, may be sim-
pler and more efficient. The precedence diagramming method is an effective
and powerful tool, but it should be used in a reasonable and effective way.
4. Computer programs, to the best of the author's knowledge, either do not
give the user the choice of (interruptible or contiguous activities) or allow it
only at the entire project level only. In the latter case, the user must decide
whether all activities are interruptible or contiguous (although the user can
choose the contiguous option, then manually interrupt and resume certain
activities). Real-life activities are not exactly one way or the other. This puts
the responsibility back into the scheduler's hands (remember the discussion on
the scheduler's qualifications at the end of Chapter 1). He or she must make
intelligent and informed decisions that should align the schedule assumptions
with reality as closely as possible within the limitations of computer programs
and practicality. Remember, it is the human being behind the computer, not
the computer itself, who makes the important decisions.