This is the default Effort Mode - the 'Original estimate' is evenly distributed between the working days in task period. The non-working days are ignored in the calculation.
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You can stretch a task to avoid over-allocation. To do that, drag and drop the right edge of the task:
You can also switch to the 'Teams' view and assign a team comprising of multiple members who will work on that task. For example, the Team Smartwatch has four members and has a 32h/d capacity, which means that we can reduce duration of the task to three days and still be left with some remaining capacity:
Warnings
Warnings can help you in resolving the most common problems. To enable Warnings go to View > Warnings. If a task does not have an Original Estimate available, a red line contours the Task (if Warnings are enabled). Click on the task to show the warning in task detail dialog:
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