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A brief history of Scheduling

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Samer Zawaydeh
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Dear Rafael,

The base 21 idea gave me a good laugh. Thank you.

With the help of google and few ideas looking at a schedule in front of me, I decided to find out the history of paper, mathematics, electricity, computing tools, CPM, and here are the findings:

Paper:
1. Early people discovered that they could make simple drawings on the walls of caves, which was a great place for recording thoughts, but wasn’t portable.
2. About 5,000 years ago, Egyptians created "sheets" of papyrus by harvesting, peeling and slicing the plant into strips
3. 3,000 years. The person credited with inventing paper is a Chinese man named Ts’ai Lun.
4. 10th century, Arabians were substituting linen fibers for wood and bamboo, creating a finer sheet of paper
5. In 1448, Johannes Gutenberg, a German, was credited with inventing the printing press


Tools
1. The original compact calculator was the abacus, developed in China in the ninth century.
2. The young French mathematician Blaise Pascal (1623-1662) invented the first adding machine in 1642, a clever device driven by gears and capable of performing mechanical addition and subtraction.
3. The first commercially successful adding machine was developed in 1886 by William Seward Burroughs (1855-1898).
4. The "Millionaire," a machine invented by Otto Steiger in 1894, was the first adding machine also capable of direct multiplication.
5. The Atanasoff–Berry Computer (ABC) was the first electronic digital computing device.[1] Conceived in 1937, the machine was not programmable, being designed only to solve systems of linear equations.
6. The hand-held pocket calculator was invented at Texas Instruments, Incorporated (TI) in 1966 by a development team which included Jerry D. Merryman, James H. Van Tassel and Jack St. Clair Kilby

The numbers:
1. The Arabic numerals or Hindu numerals or Hindu-Arabic numerals are the ten digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9). The decimal Hindu-Arabic numeral system was invented in India around 500 AD.

2. While the word algebra comes from the Arabic language (al-jabr, الجبر literally, restoration) and much of its methods from Arabic/Islamic mathematics, its roots can be traced to earlier traditions, most notably ancient Indian mathematics

2. Prehistoric mathematics: The origins of mathematical thought lie in the concepts of number, magnitude, and form.[8] Modern studies of animal cognition have shown that these concepts are not unique to humans. Such concepts would have been part of everyday life in hunter-gatherer societies. That the concept of number evolved gradually over time is evident in that some languages today preserve the distinction between "one", "two", and "many", but not of numbers larger than two.[8]
The oldest known mathematical object is the Lebombo bone, discovered in the Lebombo mountains of Swaziland and dated to approximately 35,000 BC.[9] It consists of 29 distinct notches deliberately cut into a baboon’s fibula.[10] There is evidence that women used counting to keep track of their menstrual cycles; 28 to 30 scratches on bone or stone, followed by a distinctive marker.[11] Also prehistoric artifacts discovered in Africa and France, dated between 35,000 and 20,000 years old,[12] suggest early attempts to quantify time.[13]
The Ishango bone, found near the headwaters of the Nile river (northeastern Congo), may be as much as 20,000 years old and consists of a series of tally marks carved in three columns running the length of the bone. Common interpretations are that the Ishango bone shows either the earliest known demonstration of sequences of prime numbers[10] or a six month lunar calendar.[14] Predynastic Egyptians of the 5th millennium BC pictorially represented geometric designs. It has been claimed that megalithic monuments in England and Scotland, dating from the 3rd millennium BC, incorporate geometric ideas such as circles, ellipses, and Pythagorean triples in their design.[15]

4. The most ancient mathematical texts available are Plimpton 322 (Babylonian mathematics c. 1900 BC),[1] the Rhind Mathematical Papyrus (Egyptian mathematics c. 2000-1800 BC)[2] and the Moscow Mathematical Papyrus (Egyptian mathematics c. 1890 BC). All of these texts concern the so-called Pythagorean theorem, which seems to be the most ancient and widespread mathematical development after basic arithmetic and geometry.


Electricity
1. Benjamin Franklin and Electricity In June of 1752, he performed his famous kite experiment, drawing down electricity from the clouds and charging a Leyden jar from the key at the end of the string.
2. Thomas Edison’s greatest challenge was the development of a practical incandescent, electric light. Contrary to popular belief, he didn’t "invent" the lightbulb, but rather he improved upon a 50-year-old idea. In 1879, using lower current electricity, a small carbonized filament, and an improved vacuum inside the globe, he was able to produce a reliable, long-lasting source of light.

CPM

CPM was the discovery of M.R.Walker of E.I.Du Pont de Nemours & Co. and J.E.Kelly of Remington Rand, circa 1957. The computation was designed for the UNIVAC-I computer. The first test was made in 1958, when CPM was applied to the construction of a new chemical plant. In March 1959, the method was applied to a maintenance shut-down at the Du Pont works in Louisville, Kentucky. Unproductive time was reduced from 125 to 93 hours

Now we are using all of the above to save time and money on our construction projects. Now I have to say that my favorite was discovering tha the oldest known mathematical object is the "Lebombo bone".

With kind regards,

Samer
Mike Testro
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Hi All

The standard abacus is a marvelous calculating machine - I never mastered it although I tried.

I once worked with a Japanese company in Baghdad and the Project manager did all his calculations on an abacus.

The European engineers were intrigued because thay used somewhat rudimentary calculators from Texas Instruments. (this was in the late 80’s pre computers)

I set up a challenge of abacus v calculator with a somewhat complex calculation - something like:

((197*42)/18)+(14.57*28.6)=??

The abacus won by a fair margin to 2 decimal places - 876.37.

Best regards

Mike Testro
Rafael Davila
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Samer,

About the Abacus thanks for highliting about the decimal point is amazing. And they only used base 20, imagine if using base 21 (boys edition abacus).

Best regards,
Rafael
Samer Zawaydeh
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Dear Rafael,

Thank you for your kind reply. I think that the softwares that we have nowadays are doing a great job at solving problems. And I hope that their black boxes are programmed correctly.

I saw that you referred to the abacus earlier and that it is not designed to solve the decimal points. So I started a small google search and found the following the you might find interesting about the accuracy of "human" before the word computer came to existance:

http://en.wikipedia.org/wiki/Abacus
" Native American abaci
.....
Altogether, there are 13 rows with 7 beads in each one, which makes up 91 beads in each Nepohualtzintzin. This is a basic number to understand the close relation conceived between the exact accounts and the natural phenomena. This is so that one Nepohualtzintzin (91) represents the number of days that a season of the year lasts, two Nepohualtzitzin (182) is the number of days of the corn’s cycle, from its sowing to its harvest, three Nepohualtzintzin (273) is the number of days of a baby’s gestation, and four Nepohualtzintzin (364) complete a cycle and approximate a year (1 1/4 days short). It is worth to mention that in the Nepohualtzintzin, amounts in the rank from 10 to the 18 can be calculated, with floating point, which allows calculating stellar as well as infinitesimal amounts with absolute precision."

Now this is the first time that I read that article, but I found it interesting that they are using "floating" and "absolute precision" for a systm that was invented by humans 4000 years ago.

If you dig a little deeper and click on the Mayan culture and CONSTRUCTION, you will find the following:

"The Classic period (c. 250–900 AD) witnessed the peak of large-scale construction and urbanism, the recording of monumental inscriptions, and a period of significant intellectual and artistic development, particularly in the southern lowland regions.[9] They developed an agriculturally intensive, city-centered empire consisting of numerous independent city-states. This includes the well-known cities of Tikal, Palenque, Copán and Calakmul, but also the lesser known Dos Pilas, Uaxactun, Altun Ha, and Bonampak, among others. The Early Classic settlement distribution in the northern Maya lowlands is not as clearly known as the southern zone, but does include a number of population centers, such as Oxkintok, Chunchucmil, and the early occupation of Uxmal."

You will agree with me that these guys 4000 years ago, planned well and scheduled their Construction sites well. They had limited resources and were able to build structures with local materials that lasted until our present day.

With kind regards,

Samer
Rafael Davila
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Samer,

I tried to illustrate the issue on how wrong and misleading many software are by not being able to get it right within a simple two activities schedule, I don’t believe a computer is necessary to understand the five activities schedule either. Is not a black box, is an easy to verify fact.

That different software can yield different results and maybe only one can provides you with true float after resource leveling is no reason to throw to the floor these tools, they can still be of some use.

Do not throw to the floor your CPM software as if no longer wanted toys, even if not high end, even if used as a low end calculator or an abacus.

Best regards,
Rafael
Samer Zawaydeh
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Dear Mike,

Many thanks for your kind support. I highly appreciate it.
I think that you should have entered this discussion a while back, but it is not too late.

Dear All,

For me a Scheduling Programs are a big calculator. Everyone can use the +, -, *, /, = and punch in the numbers and get the right answer. Unfortunately, not everyone can juggle few thousand activities using windows and then VERIFY the right answer.

The level of mathematics envolved in programming the box is high, and an engineer (Junior or Senior) does not have the time to understand it (even if can understand it, his company is not paying him to understand it), bearing in mind that, it has to be understoond and verified by the other party. So, it is better to assume that the black box is giving the right answers until it is critical enough project to veryify the results using another black box.

History speaks for itself. Civilizations were built without computer or programs. CPM came in the 1950’s. Needless to say, that current civilizations underwent TWO world wars without computers or programs.

I can very much assure you ALL, that Engineers CAN build construction projects successfully without ANY computers or ANY Schedules. If the Romans, Egyptians, and Chinese succeeded in building Empires for hundreds and thousands of years, then my statement is valid. Can you tell me the name of the software that enabled the British Empire (largest Empire in history) to rule for hundreds of years! The answer is No. You agree with me that it required a lot of planning and scheduling. That is why, I am confident that today’s Engineers can do the same thing if they are put under similar circumistances, for the simple reason that they have more education and more understanding of Engineering than the "Engineers without Degrees" hundreds of years ago.

Let me state very clearly that the CORE purpose of a CPM software is to SAVE TIME AND MONEY. If the softwares that engineers are using these days are not providing this, then the original purpose is lost. These tools are adding more confusion and are not being used properly. Gates was successful in creating a "friendly window environment" that other are using as "input" to the black box, and "output" to view the results. Scheduling Software are like tools in the hands of users. Can a T-square draw a perfect drawing! You are mistaken to think it can. Even if it has a buzzing name.

Ultimately, scheduling tools must evolve in order to enable the user with "reasonable" experience to use the tool to save him/her time and money, and for this result to be verifed (i.e, a checking mechanism).

With kind regards,

Samer
Hi Mike,
we live in a free world and everybody can do what he/she likes if it does not harm anybody.

I can imagine that in your projects resources are unlimited, Unfortunately in most projects where we are involved there are resource restrictions and creating project schedules we cannot ignore them. Our schedules consist of many thousands activities and manual levelling I consider as a joke.

Most people just draw their schedules and their schedules do not answer to what if questions. They are almost useless. When people manage projects they manage resources and if the model does not answer to the questions on resources it does not help much.

Best Regards,
Vladimir
Mike Testro
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Hi Samer

I have had the same knockabout chat with these two eggheads on the topic of resource levelling on a number of occasions on PP.

I am with you Samer - I don’t trust any computer to make my decisions - especially when it won’t tell me what it has done to my schedule.

I now let Raf & Vlad speak to each other on their own level where they can do least harm to the rest of us.

Best regards

Mike Testro.
Samer Zawaydeh
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Dear Rafael and Vladimir,

I agree that the Schedule is very important for the "what if" analysis, and it is used for many decision making actions pertaining to recourses. Actually, this can not be done in a timely manner without these tools.

I am very much against trusting the black box without understanding its formula. The problem is that people start applying the constraints and lead and lags, calenders and local and global options without understanding the black box formula. They you have an output that is support to predict the time and cost throughout the next couple of years.

Unless you have a systematic process to verify the input, and make sure that you Model is correct, there is no way to make certain that the output is correct unless you rely on experienced engineers with prior experience in a similar project.

With kind regards,

Samer
Dear Samer,
if resources are limited, if there are financial restrictions, if logistics set restrictions on supplies and the schedule does not take this into account the schedule will be unrealistic.
The purpose of creating schedule model is to get help with decision making. If project manager can get the answers to the questions like what if we will use additional resources, what if we will get the loan, etc. using computer model then it is worth the efforts for its creation.
Resources are always limited. The client may ignore this but not the contractor.
Best Regards,
Vladimir
Rafael Davila
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Samer,

Black Box is not knowing true float after resource leveling, even on a two activities schedule Primavera (all versions), Microsoft and Asta gives you the wrong answer.

Proposing not using resource leveling functionality on thousands of activities is kind of insane.

I agree with you with regard to any software that give you wrong float after resource leveling, better do it at the 1950’s way, by hand as the 1960’s is still wrong, and worst, is misleading.

Best regards,
Rafael
Samer Zawaydeh
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Dear Vladimir and Rafael,

Thank you for your kind explanation. I am using P6.7.

Why do you want to use resource leveling? Of course the software will produce outputs depending on its programming. And that is a black box only the mother company knows.

Keep it simple and control the Schedule. Let the computer do the number crunshing for the forward and backward pass. And with a systematic trial and error, you can achieve the contractual milestones, by changing the planned activities, resources and duration.

For complex project, follow systematic procedures, and tightly monitor the input and output.

The core of CPM is intact and is the same in all softwares. The add on is what is causing numerous degrees of difficulties for people to understand, use, and explain the results. And I am very much against that. The Schedule Model should be like any other system in Engineering. Unless you can predict exactly how the model is going to behave, then it is rejected. People are submitting programs of works and they can not explain the output. This is totally unacceptable.

I think maybe in the future I should get a copy of Spider and compare results. Maybe by beginning of next year or earlier.

With kind regards,

Samer
Dear Samer,
CPM schedules will be the same if the original data are the same and the software the same way interpret these data.
For an example, ALAP activity means different for MS Project and P6 (and Spider).
But everything changes if resources are restricted. CPM does not work anymore and the levelling results that are produced by different software are not the same.
We are proud thatSpider Project calculates the best (shortest) resource constrained schedules.
Please inform me about the software that you use and I will send you the examples.
Best Regards,
Vladimir
Rafael Davila
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Samer,

For a start different software use different resource leveling algorithms, even in Spider Project you have the option of several algorithms, a truth not to shame not to hide, on the contrary to be openly exposed.

There is also another difference in computation of Early Start where this value is dragged to the right in most PDM computations but that can be modeled to be at the left under PDM computations, this is solved by P3 when you allow for activity splitting. I believe it can be better modeled under PDM without activity splitting and just to specify if drag to left or drag to right. The remaining is mathematical computations based on the different types of float. I would like it to be available not at the project level but at the activity level.

On the issue on continuous/discontinuous (non-split/split activities) the following article can serve as a start.

http://www.pmicos.org/topics/aug2006tom.pdf

As Vladimir once said AOA and PDM are just different representations of the same.

Best regards,
Rafael
Samer Zawaydeh
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Dear Rafael,

I fully agree on the resource dependencies. But I still do not agree that CPM scheduling changes from one software to another. The basics are the same, what changes you make to the choices in the input will make changes in the output.

With kind regards,

Samer
Rafael Davila
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If you still do not see the resource dependences you can add some milk by selecting Create Dependences. Thes will be shown in the Gantt diagram as dotted lines. Once again, remember these are dependences that can change as the schedule is updated and time demand for resources changes. These are not fixed and in any way will interfere with true resource leveling.

Resource Dependancies

Best regards,
Rafael
Rafael Davila
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RESC V4

MILK TO THE OTHER SOFTWARE AS IN SPIDER PROJECT YOU GET TRUE FLOAT
AFTER RESOURCE LEVELING.
Mike Testro
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Hi Rafael

Did you know that the Gene Kelly clip should really be called - Singin’ in the Milk.

Plain water didn’t show up on the film so they added milk to it.

The actual song was first performed back in 1926.

Best regards

Mike Testro
Samer Zawaydeh
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Dear Rafael,

Can you please make it a 5 activity sample with start and finish milestone, and confirm that you are scheduling.

I am finding it very hard to accept that CPM is changing from one software to another. The basic programming must be the same. In my opinion, problems occur with the selection of option.

With kind regards,

Samer
Rafael Davila
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True RC Float
Spider 2
Rafael Davila
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Mike,

You can have a thousand activities delayed by resource constraining and none critical. That resource leveling delayed an activity does not means the activity became critical.

But just imagine my two activities schedule and adding a third activity not tied to any other, not requiring any resource and with 20 days duration. After resource leveling one of the remaining two activities will be delayed but none of these two will be critical, of course most software will still show wrong float for these activities.

Best regards,
Rafael

Vezi mai multe video din Muzica
PS. Mike if you have not seen the movie Green Zone you will find another impersonator of a PP member.
Mike Testro
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Hi Rafael

In Powerproject if you have set up a resource leveling operation - which is very rarely in my case - on each reschedule a note comes up which tells you which of the levelled tasks have not been moved and have therefore affected the critical path.

Not as good as Spider I agree.

Best regards

Mike Testro

PS I’m gonna kill that pesky Gene Kelly impersonator.
Rafael Davila
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Sammer,

As to keep it simple limit the schedule to 2 activities, a single resource and a single calendar, it still will be wrong. The wrong output from SureTrak was as per 2 activities, a single resource and a single calendar.

Another way to find out the computations are wrong is if some activities are missing is by filtering for critical activities and if you see a discontinuous path most probably the cheap software left some out because is calculating wrong float for resource critical tasks.

Meanwhile to make it easier I will look for a single activity sample job where the single activity is not critical, of course without setting a job finish constraint or any other dirty trick to bypass computations.

Best regards,
Rafael
Dancing frog
Samer Zawaydeh
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Dear Rafael,

I will delay answering your question until I read the manuals. You can assign a Calender for each resource. There are so many options for each activity, and unless you understand the basic programming theory, I do not think I can answer the question correctly.

With kind regards,

Samer
Rafael Davila
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The following illustrates how wrong the computations for float on a simple 2 activities job can be.

WRONG FLOAT

Best regards,
Rafael
Rafael Davila
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Samer,

I believe in P6 you can schedle an activity without the use of steps, this is a functionality with other purposes, but I am not a P6 user.

If you have P6 you can try with the following monstruous 2 activities job.

Schedule a 2 activities network, not tied one to each other by precedence logic but sharing a limited resource.

For example:

Activity A – 5 days
Activity B - 5 days
Both activities claiming for Resource A of which only one is availble.

Most software under resource leveling will schedule A and B at different time, the first one depending on your priorities selection. This is ok up to this point, but the problem is most will show float of 5 days on the first activity while a delay in this activity will delay the completion of your schedule.

Imagine that you as a Project Manager look at the available float as per your CPM schedule and start paying attention to those shown as critical and even start moving resources from those showing some float as to keep under control those showing no float. Because most software under resource constrained schedule will show the wrong float for resource critical activities you most probably will end up moving resources precisely from the wrong activities. You either will discover too late it was wrong or start doubting about the CPM float display. Well better start doubting about the CPM float display and either buy a glass ball or software capable of showing resource critical float.

You got to know what is driving your schedule in order to take control.

Best regards,
Rafael
Samer Zawaydeh
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Dear Rafael,

Are you sure that Primavera is not calculating a resource critical path? Currently each activity has "Steps" into it. And each step can have so many weights associated with its completion and that surely affects the float on each activity.

With kind regards,

Samer
Thank you, Samer,
the paper is interesting and I found it on another site http://www.mosaicprojects.com.au/PDF_Papers/P042_History%20of%20Scheduin....
It is interesting that Russian joint venture of ICL (ICL-KPO) is one of our Russian distributors.

Rafael,
Spider Project calculates Resource Critical Path and true resource constrained floats since 1993 when it appeared on the market. In 1996 I had made presentations at IPMA Congress in Paris and PMI Conference in Boston speaking about Resource Critical Path and paying special attention to the wrong total floats calculated by known software packages when resources are constrained. Since then nothing had changed except the invention of Critical Chain (other name of Resource Critical Path).

There is a lot to write about resource constrained scheduling but I expect that Patrick decided to make very brief guide.
I believe that an author of this paper is PP member.

Best Regards,
Vladimir
Rafael Davila
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http://www.pmforum.org/library/papers/2006/A_Brief_History_of_Scheduling...

- "Conclusions
The evolution of scheduling has been a fascinating journey:
• Kelley and Walker set out to solve the time-cost conundrum and invented CPM. For most organizations the resolution of time-cost issues is still in the ‘too hard’ basket (although
SPIDER offers an interesting solution)!"

There is no mention as to the fact that few software, if any, other than Spider can provide you with true Float after resource constraining. This has been known for decades at the college level thesis but not at a practical software application until now.

Maybe the article was written before this functionality was available in Spider.

Best regards,
Rafael
Samer Zawaydeh
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Dear Anoon,

No Solitaire :) but I will update you in good time.

With best regards,

Samer
Anoon Iimos
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Hi Samer,

Sorry, I can’t, but if you are going to ask me about another "spider" - Spider Solitaire, then I would say that I’m an expert.

Regards