Operations Management For Dummies, 2nd Edition
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With a critical path diagram complete, you can calculate a timing estimate for your operations project. Follow these steps to perform a forward pass analysis, which defines the earliest start times and earliest finish times for each activity. This also identifies the earliest finish time for the project as a whole.

A complete critical path diagram.
  1. Begin by writing the earliest start (ES) time (which is customarily 0) in the upper-left corner of the start node.

  2. Add the duration of the start node (0 days) to determine the earliest finish (EF) time for the start node and mark it in the upper-right corner of the node.

    That is, EF = ES + Duration.

  3. All the activities that can begin right away (activities with no predecessors) have an ES time of 0 because they are successors to the start node.

    B’s ES time is 0, as noted in the upper-left corner. The duration of this activity is 21, which means that B’s EF Time = ES Time + Duration = 0 + 21 days = 21 days. This information is noted in the upper-right corner of the activity’s node.

  4. Subsequent activities, operations with a predecessor, have an ES time that’s equal to the earliest finish time of its predecessor.

    This means that Activity C’s ES is 21. Its duration is 7, so C’s EF time is 28.

  5. If an activity has two predecessors, then its ES is the later of the two predecessor’s EF times.

    Activity F has two predecessors, B and C, with earliest finish times of 21 and 28, respectively. So F’s ES is 28. Its EF time is 28 + 0.5 = 28.5 days.

  6. Continue noting the ES and EF times for all the activities on the diagram.

    Note an EF time on the End node. The EF time, 31.2 days, is the minimum time needed to complete the project.

About This Article

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About the book authors:

Mary Ann Anderson is a consultant in supply chain management and operations strategy. Edward Anderson is an associate professor of operations management at the University of Texas McCombs School of Business. Geoffrey Parker is a professor of management science at the A. B. Freeman School of Business at Tulane University.

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