Updating/ progressing a typical Primavera P6 Schedule...
...and correctly defining the schedule’s activity type
1. General Comments
In a nutshell, for a construction schedule, one can update started activities by
either taking the percentage complete only (if the activity % complete is set to
"Duration") or by entering re-forecast completion dates (and at the same time updating
the activity's physical % complete).
2. Schedule Updating
More often than not, frequently, the activities' percentage complete type (Details/
General tab) will be selected as "Duration" and % complete dates will be given to
the scheduler and he will then enter these into the schedule.
One advantage of this set-up is updates are quick and updated forecast dates are
automatically re-calculated by the software.
However, for construction projects, this methodology if we are not careful can yield
wrong dates. Using the "Duration" as the % complete is suitable for activities made
up of equal units of equal duration, and not for activities of varying complexity/
duration as these are progressed.
Figure 01: Definition of % Complete Type.
For example let's say we're welding 10 identical spools in a fabrication shop, then
we could reasonably expect the duration for the welding of each spool to be approximately
the same (assuming no great variation in productivity moving from the first to the
last welded spool). Now, as the counter-case, let's assume the tiling of a floor.
The wide open areas will be easy to do and physical percentage complete (measurement
based on surface area) will progress quickly. However, the last remaining % complete,
will take a disproportionally amount of time, given that tiles will have to be carefully
cut and fixed along walls and fixtures.
Hence in the former example, defining the activity's completion type as "Duration",
and re-scheduling based only of % complete will be correct, whereas for the later
example the more appropriate methodology would be to define the completion type as
"Physical", enter these percentages for each progressed activity, all well forecast
completion dates (instead of relying on the software to calculate these).
For a construction schedule, better accuracy (by the way of the correct progressing
of activities and the calculation of the forecast completion dates) can be achieved
by manually entering forecast completion dates (these either to be calculated by
the planner/ scheduler or given to him by the relevant person involved in the supervision
of the given works).
So two sets of data would need to be fed to the schedule: both "Physical" % complete,
and forecast completion dates.
Otherwise, to use the "Duration" % complete will lead to wrong forecast dates. If
still in doubt, let us just think of how many times we've seen activities with say
95+% complete for weeks and weeks, with the forecast completion date sliding on every
single schedule update? The activity's physical progress might truly be as stated
e.g. 95+%, however the last 5% can take anything from 5% to potentially 100% (or
more!) of the original activity's duration.