NASA-Systems Engineering

# Activities that are not on the critical path have a

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Unformatted text preview: vel activity using the third relationship described above. Unless one is hammocking, the most common relationship used in precedence diagrams is the second one mentioned above. The activity-on-arrow format can represent the identical time-precedence logic as a precedence diagram by creating artificial events and activities as needed. 4.4.3 Establishing a Network Schedule Scheduling begins with project-level schedule objectives for delivering the products described in the upper levels of the WBS. To develop network schedules that are consistent with the project's objectives, the following six steps are applied to each cost account at the lowest available level of the WBS. Step 1: Identify activities and dependencies needed to complete each WBS element. Enough activities should be identified to show exact schedule dependencies between activities and other WBS elements. It is not uncommon to have about 100 activities identified for the first year of a Critical Path and Float Calculation The critical path is the sequence of activities that will take the longest to accomplish. Activities that are not on the critical path have a certain amount of time that they can be delayed until they, too are on a critical path. This time is called float. There are two types of float, path float and free float. Path float is where a sequence of activities collectively have float. If there is a delay in an activity in this sequence, then the path float for all subsequent activities is reduced by that amount. Free float exists when a delay in an activity will have no effect on any other activity. For example, if activity A can be finished in 2 days, and activity B requires 5 days, and activity C requires completion of both A and B. then A would have 3 days of free float. Float is valuable. Path float should be conserved where possible, so that a reserve exists for future activities. Conservation is much less important for free float. To determine the critical path, there is first a "forward pass" where the earliest start time of each activity is calculated. The ti...
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