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CPM HOW IT IS CREATED

7 replies [Last post]
ulysses garcia
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Hi Guys,

In my school days I learned the CPM is created as a result of forward and backward pass computation.

In this todays modern world with the aide of powerfull computers the CPM is totally violated in a sense it does not obey the proper rule of planning.

What i want to say , others are making or they first identify by themselselves where the CPM will run thru along the schedule not a CPM as a result of a computation.

My Question: Can CPM be indentify first or after computation

Replies

Rav B
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Posts: 1027
Point is being discussed in parallel forum already

http://www.planningplanet.com/forum/forum_post.asp?fid=1&Cat=2&Top=34159

Cheers,

Raviraj
Richard Spedding
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Ulysses,

Certainly in building, which is my experience, I expect to find the critical path running through particular parts of the project.
Typically (without constraints from design and procurement r any sectional completions) I would expect the Critical Path to start with earthworks and piling, go through the sub-structure and the building frame, then into the building envelope into the services fitting out and finally into commissioning to final hand over. If it did not follow that path, I would look at the discrepancies first to make sure the particular logic / constraints were input correctly.
I am sure other disciplines have similar rules of thumb which enables a rapid reality check.

It does not matter whether one uses manual or electronic calculation methods, the answer will be the same.
Andrew Dick
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Ulysses,
I’m afarid I don’t fully understand where you want to go with the CPM.


As far as assumptions go, the whole project is built on assumptions and only ever a plan until it is complete.

We can only ever assume that the durations we have are correct and based on the best information availible at the time. The resources are considered as a result of the detailed planning, and an assumption of both the quantity of and the type of resources required to carry out the activity.

The critical path no matter how it is calculated, either manually or by the software, is an assumption based on calculations derrived from the information put into the plan. As is normal with a project the critical path will vary during the execution of the project and will be calculated as a result of the information availible at the time (status).

If there is something else that you were meaning from your posts please explain further and we will all try and assist you.

Andy
ulysses garcia
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Groups: GPC Qatar
HI ANDREW,

Your viewpoint is acceptable using schedulling software. How about doing it in manual calculation i think it won’t work.

I believed there are three thing what we call it assumption,guess in planning using software. 1. assume duration 2. assume resources, 3. assume CPM this is new.
Anoon Iimos
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Andrew,

what’s a cut lunch?
Andrew Dick
User offline. Last seen 4 years 19 weeks ago. Offline
Joined: 14 Feb 2007
Posts: 295
Ulysses,
In my experience there is always someone on the project who will claim to know where the critical path should be. This assumption may be based on gut feel or personal knowledge.
Either way as a planner it is something that we should hone in on, as if it is to be true the analysis should identify it to be true.
If after analysis the critical path doesn’t match what was predicted, and the person that predicted it still beleives that they were correct, you need to start the detective work. If the person who suggested the critical path isn’t happy with the end result you will quickly loose their favour.

So when considering analysis of the critical path based on someones assumption it is important to ask them lots of questions as to why they think the critical path should be where they say.
Some of the reasons behind the discrepency could be the built in logic being incorrect, the durations of some activities being incorrect, but, more often than not it will be a combination of the 2 of these things and most importantly a missing peice of information known only to the individual who is questioning the critical path.

Reasons for this missing peice of information can be as simple as the person not thinking it was important or a simple oversight on someones behalf.

It is very important that as a planner you are part magician and part detective, that you can ask the same question 5 different ways, and most importantly have faith in, and an understanding of, the answers you get out of the schedule.

If you still cant get the person to beleive the answer, give them a network chart of the schedule, a calculator & a cut lunch, explain how to calculate a critical path and let them prove you wrong.

Andy
Bernard Ertl
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In this todays modern world with the aide of powerfull computers the CPM is totally violated in a sense it does not obey the proper rule of planning.

What i want to say , others are making or they first identify by themselselves where the CPM will run thru along the schedule not a CPM as a result of a computation.

My Question: Can CPM be indentify first or after computation

CPM schedules are still calculated with forward and backward passes. The algorithms are complicated now with multiple calendars and possibly post-calculation leveling, but the core process is still the same.

Whether or not a schedule is built to suit expectations or expectations are adjusted after proper CPM analysis will depend upon the project management culture of your organization.

Bernard Ertl
InterPlan Systems