(an insight into the nature of *deterministic* schedules)
Your schedule is based on deterministic dates
At least 50% of the times your schedule will be late. That may come as a surprise,
but if we think about it, actually the reason is simple: the schedule is made of
many activities, and the duration for each activity is deterministic, meaning that
it is a single point duration; the durations are averages (and even then, these averages
are not consistently defined: are they the mode, the median or the mean averages?).
Example - Driving to Work: How long does it take?
Let us take as an example “travel to work” as an activity. The duration for this
activity might be say 25 minutes in a good day, 35 minutes on average or 60 minutes
in a bad day with heavy rain or snow. So for this activity (assuming mean and median
to be the same) 50% of the time you’ll arrive to work early, and 50% of the time
One must ensure there’s built-in contingency into the schedule. Ideally you’ll want
also run a PERT analysis if you have the software. But the important thing is to
be mindful of duration averages and the need to have some extra leg room in your
Something else to bear in mind: The schedule is *not* real. It is *not* an exact
representation of reality, but rather a very simplified – and therefore imperfect
– representation. It is not an exact science, but actually to some extent an art.
However used correctly, it’s a very useful tool to analyze
the execution plan, criticalities, concerns and risks. Furthermore the schedule is
very helpful in forcing one to think about these and as a medium of communication.
Tip: The scheduler should not get lost in the finer details and assume an unwarranted
confidence, but maintain a holistic view. One should avoid not being able to see
the forest for the trees. A good scheduler will be cognizant of what the schedule
is and what is not, and will communicate identified criticalities and potential issues
and concerns to those executing the project so that corrective action and mitigations
are put in place, so that the project is completed as per the planned target date
(or as near as possible to the target date) without delays that could have been avoided
with careful planning.
Example of Schedule Delays:
Data from MCR (An AT&T Company) Smallsat Schedule History: Months from Development
Contract Award to Launch.