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Overlapping Activities

5 replies [Last post]
Sun, 2007-09-23 00:53
Raphael M. Dua
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Does anybody in the scheduling community remember the Ladder Technique for Schedule Compression for overlapping activties to shorten the critical path
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Mon, 2007-09-24 08:35
#1
Oliver Melling
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Raf,

Do you think that so many companies, such as NASA, VINCI, the whole UK nuclear industry, Bechtel, United Utilities, Walt Disney (and there are hundreds more) would invest millions in software, licences and training, for a product that doesn’t deliver the required level of accuracy for tracking/managing their business?

The Sarbanes -Oxley ACT is about financial transparency not the estimated accuracy of perceived performance.

As i mentioned earlier, SPI/CPI are only indidcators as EVM is a project management tool not a thourougbread financial accounting tool.
The BCWS (PV) is mapped to an estimated baseline programme by Resource/Expense loading and as estimates aren’t always broken down to activity level, the proportion of the spread is also an estimate.
The odd day out counts to me, but only because i know its there! The client wants to know about this stuff sure, but do they want to know it enough to do a manual PERT analysis on a 8000 activity programme?

Regards,

Oliver
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Mon, 2007-09-24 06:54
#2
Raphael M. Dua
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Oliver

I work on all sorts of projects from as small as $AUD% million to USD $% billion
Mostly government jobs and I can assure you the client does care about the inaccuracies.
The US government enacted the Sarbanes -Oxley ACT and in Aus we have CLERP9 which states you willlknow exactly how the numbers you quote to the public and your shareholders were arrived at.
With projects costing 2 to 3 million per day I am amazed that you are happy having an error or $10 to 15 million or so.
Governance is roaring in strong and loud and if we as Planners and schedulers continue to use software which allows poor results and poor planning, then why do we bother

Polishing to the Nth degree does not anything any more accurate.
it has to be right first time everytime, so use products which get it right would seem to me to be a sensible thing to do.

You can’t beat the old Mark One eyeball, using pencil and paper
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Mon, 2007-09-24 06:02
#3
Oliver Melling
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Raf,

Do you think that the client cares about lag drag?

I mean, EV is far better as a management tool on multi-million pound contracts, which usually last 6 months at least.

99 percent of the time the person managing the contract on behalf of the client will only see a summary programme or hardcopy of the programme, thus they would have to do a PERT analysis to discover the odd day here or there.

I have worked with P5 planners who don’t use calendars properly and randomly select duration type for their activities, leading to being the odd week or two out!

EVM is a world of performance INDICATORS, that show where the project is going, i don’t think it needs to be polished to the Nth degree.

Regards,

Oliver
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Sun, 2007-09-23 23:43
#4
Raphael M. Dua
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Ashraf
Thanks I already knew that, Ladders were an Arrow Diagram Technique, not Precedence. The problem with using Start to Start and Finish to Finish is lag drag.
If you do not know what lag drag is, the following might explain

Two Activties exist, one call "A" and the other "B"
A is 10 days in duration and B has a duration of 5
There is a SS of 1 from A to B and a FF of 1 to B

When you calculate from the start of A (= 0) to end of A, the EF is 10, now calculate the EF for the FF, and we have 10 +1 =11.
Go back to start of A, ie 0. The EF for the SS to B is 1. Thus the ES for B is also 1, add the duration to get the EF , ie 1 = 5 =6. Ah, but B can’t finish until 11, because of the FF relationship.
So Primavera and Open Plan subtract the duration from the EF of Activity B and show the ES as 6, that is 11 -5 =6.
But B can start as early as 1, but cannot finish until 11. Thus there is Free Float in the activtity, but as I just said Primavera and OPP make the ES of B 6. Thus you have just experienced lag drag. TheES of B has been dragged to the right.

This is wrong, so Primavera and OPP have a switch which causes the ES to be pulled back to ES = 1. This is achieved by increasing the duration or elapsed time, which is quite wrong.

The only correct form we were able to get coreect computations was to use the Ladder technique in Arrow format. Ladders go back to 1962-64

See HS Woodgate’s book "Planning by Network 1968 page 41
Dennis Lock’s book "Project Management 1989 page 103

But then that is another story

Raf
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Sun, 2007-09-23 07:48
#5
ashraf alawady
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You can use SS and FF relationships it will lead to overlap the activities and shorten the durations.
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