Free Critical Chain: A Business Novel by Eliyahu M. Goldratt Page A

all laugh; no student likes complicated examples. Me either.

"Suppose," I start, still not sure of the example I'm going to pick, "the project is to...to build a plant. We need to build the building and then to make it functional."

Before Ruth asks me to define "functional," I continue, "To install the electricity lines, the water and compressed air pipes, et cetera. We also need to select and contract the various vendors to build our machines, and allow the vendors enough time to build them. Once the building and the machines are ready, we can install the machines. The plant is now ready."

"Not until you've hired and trained the people," Fred must remind us.

"What's your point?" Ted is less polite than I would have been. "Plenty of other details are not mentioned here, either."

"Let's keep the example simple," I tell Fred, and invite him to come to the board and draw the relevant PERT chart. Confidently he comes to the front. It takes him less than two minutes to draw the diagram.

"Can you invent some time estimates for the various steps?" I ask him.

"With pleasure." Being a financial manager he cannot stop himself from asking, "Do you also want estimates of investments?"

"No need."
     

     
    I wait until he finishes and returns to his seat. "According to the numbers that Fred picked, it will take ninety days to build the building and thirty days to make it functional. A total of one hundred twenty days."
     
    "Fred, where did you get such unrealistic numbers," Ted shouts.

"Out of thin air," Fred calmly answers.

I ignore them both and continue. "To pick the vendors takes fifteen days."

"Only in Fred's dreams."

I give Ted a look. He signals, "Sorry." I finish my sentence, "And the time it will take them to supply is another ninety days. The installation of machines takes an additional thirty days. What is the critical path?"

"The building." Ted is very vocal today.

"Why?"

"Because, according to Fred's ridiculous numbers, it takes one hundred twenty days to prepare the building while the machines are ready in one hundred five days."

"You are too hasty," I tell him. "Critical path is defined as the longest chain of dependent steps. Longest in time, of course."

"I know," he impatiently says. Then more slowly, "The critical path is the path through the steps of building the building, making it functional and installing the machines in it. A total of one hundred fifty days."

"The critical path," I remind the class, "determines the time it will take to finish the project. Any delay on the critical path will delay the completion of the project. That's why the project manager must focus on it."

Nobody has a problem with what I've said. No wonder, considering their experience in projects.

"If we call the time we start the critical path ‘time zero,' the project is planned to be finished at time one hundred and fifty. When should we start the other path? When should we start picking the vendors for the machines?"

"There is no rush there," Brian volunteers an answer. "We can start picking the vendors at time fifteen."

"What?" Ted exclaims.

I signal Ted to calm down and ask Brian to come to the board and draw the corresponding Gantt chart. He does it without any difficulty.
     

     
    "Brian chose the late start for picking the vendors," I say. "But, as we all heard, Ted probably has another suggestion. But Ted, rather than giving us a whole speech, go to the board and draw your Gantt chart."
     
    That throws him off balance for a second, but just for a second. When his chart is done he turns and starts attacking Brian, "I don't know what's gotten into you. You are going to tell me that in the projects you manage you really start at the latest possible time? No wonder your projects are late. You've got spare time, take it! That's my motto."
    "Fine, Ted," I calm him down. "But will you please go back to your seat so we all can see what you drew?
     

     
    "Gantt charts, unlike PERT diagrams, involve decisions," I