CPM - A LOUSY TOOL

Chris



I think that in the absence of any contrition or change on the part of those who upset us, we have just got to live with it and perhaps not react as strongly as we do - a lot of the comments seem designed to provoke reaction (and they succeed, even with me)

All in all the forum is very useful to many planners world-wide, and it would be a shame to change something that works becasue some anarchists try to butt in.



(My spelling too on occasion Clive! - Is it true about big fingers?)

Nieman,



I completely agree with your point about having a thought-out argument to back up any statements people make. Sometimes it can be useful to put forward something a bit controversial just to get people going and to see what develops. Also to say you don’t like some part of the methodology because you find it clumsy or difficult to use as that’s just an opinion which anyone is entitled to.



What is difficult to take is someone who pontificates to no purpose often venturing into the realms of the totally bizarre. In cases like this the culprit gets the mickey taken out of them, which can be great fun but may not be the best way to to deal with them. Unfortunately, I don’t have a clue as to what would be the way to go, any ideas?



Chris Oggham

I don’t mind new ideas, Vladimir, and we surely take the rise out of Charlie when he pontificates, but what I do not like is someone just saying that a generally accepted methodology is rubbish without giving us a thought-out argument to back it up!



I appreciate that language may be a problem, but believe that generally we make allowances for that (even for Clive’s spelling on occasion)

Dear collegues,

I think that we shall encourage PP members to suggest new ideas even if we disagree with them. Any discussion may lead to the new knowledge and helps to look at the known problems from the new angle. Discussion on one topis may lead to discussions on other topics and it is very good!

We shall be grateful to Uly if he will suggest some new approach even if we will not agree, even if his suggestion will be erroneous.

Regards,

Vladimir

Thats more a statement than a subject may i suggest something like



’The Trans-Continental Migration of Scottish Planning Resources between 1988-2006’

I have another one albeit much simpler



“ ORNITHOLOGICAL SPECIMENS OF IDENTICAL PLUMAGE CONGREGATE CONCURRENTLY”

How about the problem with logic?

What topic should we digress with now??

Here here,



I wondered wht the middle of this thread started going on about estimating durations! Thought there was something i was missing!

Quite right!!!!!

hi,



CPM is not a method to estimate duration/resource.



CPM just calculates dates/float based on the durations and logics you told her, and give you a critical path. So what’s wrong with CPM? you give her wrong duration/logic, she give you wrong critical path.



IMO, the key point for CPM is logic/relationship. with logic you can do the calculation, if the duration/logic is wrong, anyway you will get the result,but not correct. without logic you can’t do any calculation.



so people did a lot to get more accurate duration/logic, e.g. link duration to resource/productivity, resource leveling...



but all these does not change the core of CPM

In simple words,



Two types are:



--> Resource Driven activities

--> Non-Resource Driven Activities



Hammock is a rolled up task level and milestone is an achievement of activity or group of activity having ZERO DURATION.



So, in TOTO, U and James were trying to say d same thing in different terms.



Lets wait and watch, what ULY is going serve for all of us.



Cheers,

Hi Raviraj,

there are two major types of activities:

1) Type Duration means that its Duration is an initial information and does not depend on assigned resources,

2) Type Productivity means that its Quantity of work that can be measured in physical units OR manhours is an initial information and duration depends on quantity and productivity of assigned resources.

There are also milestones and hammocks (LOE activities) - additional types.



It is very interesting what will be suggested as an alternative to CPM. So let’s wait. Any discussion on scheduling methods is useful.



Regards,

Vladimir

Well Guys,



How somebody can say that manhours is usually the fundamental unit by which your resource requirements/duration will be defined or QUANTITY of work to be done is the fundamental unit.



We all know that, only one parameter cannot dictate the duration required. It can be also in terms of manpower required for an activity to be done or in terms of quantities.



e.g. If u r doing Brick-work, then it will be primarily dictated by the no. of manpowers available.



If u r doing some testing works or say concreting works, then it will be constrained by the equipments available.



There is no point in saying that ONLY one of the above will dictate the duration required.



If u doing brick-work, then there is an assumption that say 2 mason and 4 workers will do a job of 65 Sqm per day of 2 Brick thick wall. That means it is constrained by both manpower and quantities.



The discussion is that one of the fellow on PP, has said CPM is a LOUSY tool and he has nothing to prove for that and trying to become NEWTON. Hope so, in the next decade u can find U-FLOW theory’s three laws of planning too in the books.



Cheers,

Vladimir, James

Are you sure that we are still on topic?



I’ll join. It would be a nice feature. I don’t know regulations in other countries, but in Germany workers council doesn’t allow to store skill-related informations - the skills in P3e/P5 in a software which can be accessed by people apart from HR or the direct superiors.

Regards

Dieter

Yes, I think that the difference is significant if you plan resource usage. Besides using activity volumes you can create and apply corporate norms (like production rates, material requirements per unit of volume, unit cost, etc.). Performance measurement become natural and helful for the forecast of remaining duration (hours do not show the work remaining).

There are many advantages.



Vladimir

Vladimir,



I agree with you in principle, with regard to differing crews having differing productivity (we’re all different). However, do you find that there is such a significant difference that it’s actually worth planning to THAT level of detail? (ie. with differing output rates for the same activity type.)



James.

Uly



Raviraj is right. If you want us to listen to your theory, organize your thoughts first, put it in paper then we discuss it. There’s no point in discussing issues if the arguments are not clear.



On the issue of progress indicators i.e., manhours, duration or quantities, I always have the view that these are just indicators nothing else. there’s no more realistic indicator than the other even CPM is only an indicator. It’s not realistic, only indicative. The more indicators you have, the better for the project.



I’m sure you have experienced feeling something in your nerve every time someone tells you that they know a more "realistic" way of showing progress.



Change is inevitable when managing project that’s why some people describe managing project as an iterative process. Maybe this is one of the reasons why using CPM can sometimes looks lousy. It’s not CPM that is lousy, it’s the nature of the project and different point of views of people that makes it lousy.



Se

I agree with James, but probably didn’t explain as well!



Coal-face man-hours along with a efficiency factor, and actual required hours are used more in nuclear. Its hard to put a physical volume to many of the project stages in nuclear, as much of the work varies between sites and in different physical environments.



I think physical quantities are suited more to repetitive scheduling rather planning.

I agree with James, but probably didn’t explain as well!



Coal-face man-hours along with a efficiency factor, and actual required hours are used more in nuclear. Its hard to put a physical volume to many of the project stages in nuclear, as much of the work varies between sites and in different physical environments.



I think physical quantities are suited more to repetitive scheduling rather planning.

Oliver,

estimation of manhours for the concrete resource and estimations of resource productivity is the same. If there are different resources then manhours depend on their productivities and may be different for different crews.

Measuring and planning physical volumes is natural and flexible.



Vladimir

Hi James,

I agree with "Resource output per unit time [productivity rate] (be it manhours, metres or tons etc) is what determines the duration."

Manhours is not enough because the same work can be done by different resources with different productivity.

Regards,

Vladimir

Hi Vladimir,



I just wonder whether we are going to split-hairs and start arguing about the same thing. Building a brick wall, for instance, might require 9 bricks (physical units) but who is going to build the wall: the man who is going to take 9 hours to do it. If he has done 5 hours, and still has 4 hours remaining, then he is 5/9 complete. Now, you could also define your progress by calculating the number of bricks he has laid....but this is a different story and a different thread that I was debating a couple of weeks ago.



To be correct in my terminology then, and in order to cover all industry types: Resource output per unit time [productivity rate] (be it manhours, metres or tons etc) is what determines the duration.



In my industry, the unit of measurement is usually man-hours. This is based on the fact that our physical output is entirely undefined in the conventional sense....for instance a single 3D model....where even "thinking time" has to be accounted for.



James.

Vlad,



The use of quantities is ok for high rises, roads and train tracks, but bespoke chemical/powder handling kit installation cannot be planned in this manner. The Duration of activities can be driven by manhours from estimates produced by SQEP engineers/estimaters and based upon available resource for the project.



Oliver

James,

I don’t agree with your statement "that manhours is usually the fundamental unit by which your resource requirements/duration will be defined."

The usual fundamental unit is the quantity of work to be done in the physical units (we call it volume of work and measure in meters, tons, cubic meters, pieces, etc.). Knowing assigned resource productivities and quantities we will be able to calculate activity duration. Knowing necessary duration we can calculate necessary productivity of assigned resources and thus to decide about necessary resource types and quantities.

Regards,

Vladimir

Never heard of U-Flow Theory!!! However, judging by what you’ve written, I guess that you "planned" your activity by defining the duration and then making your resources fit. That’s fine. I guess, therefore, it defines whether or not your activity lies on the CP. However, the quantity of manhours stays the same. If your output/progress rate is less (maybe because only half the resources decided to go to work) and you extraploate based on historical data, then your duration MUST extend. By recalculating, using the CPM, the activity might now be placed on the CP. However, if you planned to double the resource within the remaining original duration, then you will complete the work in accordance with the original end-date.....thus CPM will not place it on the CP. This is the whole idea of using CPM and a correctly programmed schedule to PLAN what you will do in order to achieve your objective.



On the other hand, you might have a limited resource. The resource limitation, in conjunction with the estimated manhours will result in the duration. Once again: if only half the resources decide to go to work, then your duration will double: mathematical fact!!! CPM will still correctly determine whether the activity has now moved onto the CP.



It’s all a case of chicken-and-egg. Do you define the duration first, and then acquire the resources to fit, or do you account for your resources which then defines the duration? Regardless, you still have to return to the fact that manhours is usually the fundamental unit by which your resource requirements/duration will be defined. If any of these variables change, then the result will change. If you still want to achieve a pre-defined result, such as maintaining the end-date, then you have to PLAN to forcibly change the relevant variable.



James.

Uly,



Will u plz explain in ENGLISH Literature. u r trying to combine PHYSICS with emotions. Dont prove urself, what others are writing abt u.



If u wanna say / prove something, write it precisely and correctly.



To draw a S-Curve in P3 without knowing resources, v used to allocate RESOURCE = ORIGINAL DURATION by global change and then draw the S-Curves. So, is thats ur U-FLOW theory?



Better Uly, u take ur own time, write ur viewpoints on a piece of paper and share with others for comments.



Y u r wasting TIME of so many people around and making this beautiful website a SCRAP, that will make people think of before joining the site.

Ulysses,



I really don’t know why you feel such hatred toward the CPM methodology. It is a perfectly good process if you understand the way it works….and can compile a properly resourced and linked schedule.



Your earlier post, with regard to using differential calculus and statistical distribution of the rate-of-change of progress is, actually, very interesting. However, you are forgetting one major element in all of the calculations that you are likely to perform: and that is the fact that you are trying to forecast the future, based on the statistical extrapolation of historical data. This methodology is equally as flawed and all that will happen is that you will become bogged-down in mathematical formulae that will prove to be no more accurate than the CPM that is being applied to a well-constructed and maintained programme. The so-called “flaw” is that:



1) The fundamental activity data (manhours etc.) are based on an estimate. We all know that estimates are likely to be +/- 20% (which itself is an estimate)….so I already have introduced a compounded error [making an estimate of the fundamental activity data, and then estimating that the accuracy of that data is +/-20%.]. You will still get an exact result, but that result is likely to be no more accurate than some of the simpler methodologies.



2) Previous performance is not an indicator of future performance (although there is a probability factor in that it might be). However, as soon as you introduce a probability factor, you must accept that there is a range of results. Therefore, your forecasts will lie between Y1-Y2. For the extrapolation to be valid, you must have enough historical data points to ensure validity…..and by the time you have enough historical data to be statistically valid, conditions have changed once again.



One of the big problems is that humans are totally irrational and are looking for certainty where certainty does not exist. When they themselves have to compile an estimate, they will always claim that “it’s only an estimate”. However, when someone else gives them a number, they expect it to be adhered to and written in concrete. Our expectations change in accordance with our emotional involvement with the project. If we hear that a $2 billion project went 5% over-budget, then we’d still applaud the accuracy of the estimate. However, if we were charged $1.05 for a bar of chocolate that was advertised as costing $1.00, then we’d be furious. Anyway, I digress…….



James.

To lead us to a new schedule evaluation era you will need a better leadership strategy than,



’Come brilliant people, do something amazing and we can call the uly method!’

Good luck Ulysses



When you have patented your new world beating mathematical model which can analyse resources and give us a much better management tool than CPM, please feel free to tell us mere mortals.



Until then, please keep quiet and allow us to get on with our poor unsatisfactory lives, telling the project managers that they couldn’t manage their way out of a paper bag!

the thing is, There is no other tool!

I think someone is just trying to be an einstein. but can not prove a point.

Can you even differentiate between LoB and CPM?



CPM is method of identifying the critical path.



LoB is a methed of presenting a schedule to show increased/decreased efficiency?

Guys - please forgive me if I sound a bit thick - but why are people attempting to differentiate between the various methodologies of CPM, LOB, Critical Resource etc. etc?



To me, it’s blindingly obvious that ANY WORK that has to be performed MUST be programmed IN CONJUNCTION with its RESOURCES and its LOGIC - otherwise you get a totally false picture, regardless of the methodology. There are slight airs-and-variations on this but, on the whole, the concepts are extremely simple - and anyone who doesn’t realise this should not be in the world of planning.......or have I just totally lost the plot.



James.

Clive,

if I understood it correctly people use Tilos together with Primavera and MS Project.

Spider Project was created for project resource management, it is too complicated for Line of Balance approach to scheduling. But Line of Balance project presentation is very useful and is included as one of the standard ways to present project schedules. Besides you can create and use any metrics, not only meters or stores, like stage 1, stage2, ... So it used not only for roads and high rise construction.

I hope that one day you will use Spider Project.

Regards,

Vladimir

This approach does not help when resources, finances, supplies are limited. It may be considered as an alternative to CPM when computers are not available.

Line of balance is just another way to present project schedule like Gantt Chart and Network Diagram. In Spider Project Line of Balance (Linear Diagram) is one of the standard project presentations.

CPM is a proven method to create project schedules when resources are unlimited.

With limited resources you shall calculate resource critical path (or critical chain).

What is the problem?

CPM based on logic and sense .

Ulysses



It’s one more thread from you on the same topic. Obviously you have some difficulties with CPM.

Stacy is absolutely right. I would like to add: If you use a hammer and hit your thumb instead of a nail, it was hammer’s fault, not yours?

We do not use CPM blindly, but with some intelligence, knowledge and experience.

Quite a different example: If you are in a city you never were before, of course you never use a navigation system, e.g. tomtom, well knowing that the algorithms to find a way are very similiar to CPM?

One is your private opinion, the other is best practice.

Dieter

CPM is a tool. In the right hands, it works. In the wrong hands, it won’t.



Don’t give a hammer, saw and screwdriver to a monkey and expect it to be a carpenter.



Stacy

Project Management Knowledge Base

Project Planning Info

Come ON ulysses!!!!



As planners we know that the programme is only a snapshot of one way a project can be built, at a particular moment in time.



The purpose of CPM is to advise the PM what the most critical string(s) of activities are on the PM’s programme (not the planner’s - the PM must sign off the programme and accept responsibility for operating it), so management time and effort is concentrated in the most beneficial areas. CPM is a dynamic tool, so the critical path will move as the project progresses, depending upon the success of particular activities or groups.



Don’t get depressed when some idiot PM tells you off because he doesn’t know his base from his apex. CPM will prove you to be right and him/her wrong in the long run (although he/she will not like it when it happens)as long as the programme is properly drafted and linked.