PREPARING THE SCHEDULE

Hi, Raphael.

Yes, activity Drag Cost is hugely important, and it's good that you point that out. But one has to walk before one can run! Dura Cell's question was about schedule, and so I tried to show how one can use critical path drag to compress a schedule and even to pull in a milestone that is NOT on the original critical path.

Ultimately, if one reduces an activity's drag, one should not only reduce the project duration and increase the project's expected monetary vlaue, but also reduce the activity's Drag Cost. But you are correct -- one must keep an eye on Drag Cost. The issue then would be: how much have we reduced the activity's True Cost?

If an activity has a resource budget of $30,000, a drag of 10 days and a drag cost of $5,000 per day, its True Cost is $30,000 + (5 * $10,000) = $80,000.  If we reduce its drag to 5 days, the drag cost goes down by $25,000. But if the total cost of resources goes UP from $30,000 to $60,000, the True Cost will have gone from $80,000 to $85,000! Not a good use of funds. 

Fraternally in project management,

Steve the Bajan 

Stephen,

Seems you are in the opulence, I would always look to activity drag cost, usable drag and drag location.

Just take a look at the following figure.

Some times the option is to add a shift and then min duration changes, sometimes is not possible to use a second shift. DRAG is an important metrics, same as float, but we shall always consider the alternatives and the overall impact in overall cost, job duration, safety, quality ... not all decisions can be programmed into an algorithm like if robots playing the same basketball game over and over.

Best Regards,

Rafael

Dura, this situation is not uncommon, although in my experience it is usually the customer who mandates an earlier date rather than the PM.  This sort of mandate has sometimes led to quite lucrative consulting assignments for me.

You should do the following:

1. Make your targeted activity (X) the sink activity by filtering out all tasks that are NOT its ancestors (predecessors, and predecessors of predecessors, etc. all the way back to the start).
2. Determine the critical path to X and the float of all the non-CP activities.
3. Compute the drag of all the activities/constraints on the new CP (in Spider Project, if you have it, manually if you have Primavera, which doesn't compute critical path drag).
4. Target the high drag items and figure out ways to lessen their drag through crashing or fast tracking.  If the CP changes, compute the drags of the new CP items and continue the process until the desired dates are achieved.

Hope that helps.

Fraternally in project management,

Steve the Bajan

Use Start on or After Constraints and adjust predecessors logic and activity durations until the constraint is feasible. You will need your PM to help you and if it comes out the dates are impossible for practical purposes then he might release the date to a latter date.

Real schedules have constraints, some are necessary, some are contractual requirements and some are arbitrary and perhaps unneeded. The less restriction the better your schedule can be but real life is not that easy.

Today even the dumbest scheduling software implements dates constraints, but not all are created equal, some are implemented in ways that do not make any sense, some even make the impossible possible in paper but impossible to understand. Start on or After Constraints are safe on all or most software. The issue is on "must finish/start" type constraints and on "Finish not latter than" type when the software artificially fix the late dates making it possible for late dates be earlier than early dates, incomprehensible, time travel is impossible, these shall be avoided if using such software.

You can use activities to replace the date constraints but make sure they do not have predecessors, only the start of the job, make sure you assign a separate calendar as for further changes on workdays or holidays do not affect the end of the activity. Then make sure you regularly update the activities that represent the constraints as to keep the successor desired date in place. But all this is unnecessary if you use the constraints, no need to create the activities just to make a senseless point, not a good idea.

Perhaps for other types of date constraints such as "Finish not latter than" types that are poorly implemented in most software the use of auxiliary activities makes sense in order to show criticality without tampering with impossible late dates. Must Start/Finish constraints make no scheduling sense and shall not be implemented in any way except for what-if and other temporary analysis.

Hi Dura

Do as he says but instead of using constraints add an activity to bridge the gap and call it PM Changes.

Best regards

Mike T,