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Using Fixed Duration, you set the duration of a task, and the work is distributed evenly across that duration (see Work Distribution). When updating a fixed duration task:
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With fixed duration, the amount of work that needs to be completed for a task (it's its work estimate) is divided evenly across the the duration when calculating resource usage. So if an issue's work estimate is 10 hours (1d 2h) and the task has a fixed duration of 10 working days, the issue would require 1 hour of work each day.
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