Critical Path


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Gantt Chart. Published on February 15, Read Time 3 minutes. The importance of the Critical Path In the first place, the critical path is an indicator of the earliest date a project is planned to complete. Related articles: Jan 8, What is a Gantt Chart? Oct 26, Task dependencies. Aug 7, Lead, lag, and constraints. For example, if a job has free slack, the foreman may be given some flexibility in deciding when to start the job. Even if he delays the start by an amount equal to or less than the free slack, the delay will not affect the start times or slack of succeeding jobs which is not true of jobs that have no free slack.

For an illustration of these notions, we return to our house-building example. We assume that construction begins on day zero and must be completed by day However, jobs that have positive free slack are so marked. There is one critical path, which is shown darkened in the diagram. All critical jobs on this path have total slack of three days. This would reduce the total slack of all jobs by three days, and hence reduce TS for critical jobs to zero. Thus the contractor could delay the completion of i rough wiring by two days, g the basement floor by one day, h rough plumbing by four days, r the storm drains by 12 days, and so on—without affecting succeeding jobs.

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What is Critical Path Method For in Project Management?

This is a simple application of workload smoothing: juggling the jobs with slack in order to reduce peak demands for certain skilled workers or machines. If the contractor were to effect changes in one or more of the critical jobs, by contrast, the calculations would have to be performed again. This he can easily do; but in large projects with complex sequence relationships, hand calculations are considerably more difficult and liable to error. Information concerning job times and predecessor relationships is gathered, typically, by shop foremen, scheduling clerks, or others closely associated with a project.

What Are Resource Constraints and Why Do They Matter?

It is conceivable that several kinds of errors may occur in such job data:. The predecessor relationship may contain cycles: e. The list of prerequisites for a job may include more than the immediate prerequisites; e. Job Times. An accurate estimate of total project time depends, of course, on accurate job-time data.

Critical Path (PC) Playthrough - NintendoComplete

CPM eliminates the necessity and expense of careful time studies for all jobs. Instead the following procedure can be used:. In many projects studied, it has been found that only a small fraction of jobs are critical; so it is likely that refined time studies will be needed for relatively few jobs in a project in order to arrive at a reasonably accurate estimate of the total project time. CPM thus can be used to reduce the problem of Type I errors at a small total cost.

A computer algorithm has been developed to check for errors of Types 2 and 3 above. The algorithm mentioned in footnote 4 systematically examines the set of prerequisites for each job and cancels from the set all but immediate predecessor jobs. Wrong or Missing Facts. Errors of Types 4 and 5 cannot be discovered by computer routines. Instead, manual checking perhaps by a committee is necessary to see that prerequisites are accurately reported.

The cost of carrying out a project can be readily calculated from the job data if the cost of doing each job is included in the data. If jobs are done by crews, and the speed with which the job is done depends on the crew size, then it is possible to shorten or lengthen the project time by adding or removing men from crews.

Manage your project's critical path - Project

Other means for compressing job times might also be found; but any speedup is likely to carry a price tag. If we want to shorten the project, we can assign some of the critical jobs to their crash time, and compute the corresponding direct cost. In this way it is possible to calculate the cost of completing the project in various total times, with the direct costs increasing as the over-all time decreases. Added to direct costs are certain overhead expenses which are usually allocated on the basis of total project time.

Fixed costs per project thus decrease as project time is shortened. In ordinary circumstances a combination of fixed and direct costs as a function of total project time would probably fall into the pattern shown in Exhibit VII. The minimum total cost point A would likely fall to the left of the minimum point on the direct cost curve point B indicating that the optimum project time is somewhat shorter than an analysis of direct costs only would indicate.

Other economic factors, of course, can be included in the analysis. For example, pricing might be brought in:. A large chemical company starts to build a plant for producing a new chemical. After the construction schedule and completion date are established, an important potential customer indicates a willingness to pay a premium price for the new chemical if it can be made available earlier than scheduled.

With a plot of costs correlated with total project time, the producer is able to select a new completion date such that the increased costs are met by the additional revenue offered by the customer. This effort is sparked, in part, because of the Air Force and other governmental agency requirements that contractors use these methods in planning and monitoring their work.

Here are some illustrations of progress made:. One of the present authors Wiest has developed extensions of the work-load smoothing algorithm. Indications of how smoothing can be accomplished are also made. For the manager of large projects, CPM is a powerful and flexible tool, indeed, for decision making:. Because of the above characteristics of CPM—and especially its intuitive logic and graphic appeal—it is a decision-making tool which can find wide appreciation at all levels of management. For the manager concerned with day-to-day operations in all departments, CPM enables him to measure progress or lack of it against plans and to take appropriate action quickly when needed.

And the underlying simplicity of CPM and its ability to focus attention on crucial problem areas of large projects make it an ideal tool for the top manager. On his shoulders falls the ultimate responsibility for over-all planning and coordination of such projects in the light of company-wide objectives. For a method for smoothing operations in a job shop, based on CPM and the use of slack, see F. Levy, G. Thompson, and J. An algorithm on which one such computer program is based is discussed by F.

See A. Charnes and W. Ferdinand K. Any delay to the Critical Path would directly result in the delay the overall project's schedule. The top sequence of tasks has no slack also called "float" , and therefore drives the finish date of the project. All tasks in this sequence are on the critical path and are called critical tasks.

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