Also called: activity network diagram, network diagram, activity chart, node diagram, CPM (critical path method) chart Variation: PERT (program evaluation and review technique) chart Description The arrow diagram shows the required order of tasks in a project or process, the best schedule for the entire project, and potential scheduling and resource problems and their solutions. The arrow diagram lets you calculate the "critical path" of the project. This is the flow of critical steps where delays will affect the timing of the entire project and where addition of resources can speed up the project. When to Use an Arrow Diagram Arrow Diagram Procedure Materials needed: sticky notes or cards, marking pens, large writing surface (newsprint or flipchart pages) Drawing the Network It can be useful to create a table with four columns —prior tasks, this task, simultaneous tasks, following tasks. Problem situations: Figure 1: Dummy separating simultaneous tasks Figure 2: Dummy keeping sequence correct Figure 3: Using an extra event Scheduling: Critical Path Method (CPM) For each task: Figure 4: Arrow diagram time box ES EF Total slack is the time a job could be postponed without delaying the project schedule. Total slack = LS – ES = LF – EF Free slack is the time a task could be postponed without affecting the early start of any job following it. Free slack = the earliest ES of all tasks immediately following this one – EF Excerpted from Nancy R. Tague's The Quality Toolbox, Second Edition, ASQ Quality Press, 2004, pages 100-105. Arrow Diagram Example http://asq.org/learn-about-quality/new-management-planning-tools/overview/arrow-diagram.html
Earliest
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Earliest
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Latest
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Jumat, 18 Februari 2011
Arrow Diagram
Determine the correct sequence of the tasks. Do this by asking three questions for each task:
Diagram the network of tasks. If you are using notes or cards, arrange them in sequence on a large piece of paper. Time should flow from left to right and concurrent tasks should be vertically aligned. Leave space between the cards.
Determine task times—the best estimate of the time that each task should require. Use one measuring unit (hours, days or weeks) throughout, for consistency. Write the time on each task's arrow.
Determine the "critical path," the longest path from the beginning to the end of the project. Mark the critical path with a heavy line or color. Calculate the length of the critical path: the sum of all the task times on the path.
Calculate the earliest times each task can start and finish, based on how long preceding tasks take. These are called earliest start (ES) and earliest finish (EF). Start with the first task, where ES = 0, and work forward. Draw a square divided into four quadrants, as in Figure 4. Write the ES in the top left box and the EF in the top right.
Calculate the latest times each task can start and finish without upsetting the project schedule, based on how long later tasks will take. These are called latest start (LS) and latest finish (LF). Start from the last task, where the latest finish is the project deadline, and work backwards. Write the LS in the lower left box and the LF in the lower right box.
Calculate slack times for each task and for the entire project.
Diposting oleh Irika Widiasanti di 16.10
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