For project managers assigning tasks and resources to a schedule, you will see a simple calculation made on every task which may be confusing at first. It's not confusing at all once you examine this simple formula.
Task Work Hours ÷ (Task Duration x Resource available hours per day)
Which value is calculated based on the other two can be modified by choosing one of these values as the auto-calculate option:
Whichever option is chosen here is the value that will be calculated based on the other two values.
% of Resource Workday: This calculation allows the project manager to set a schedule based on the duration of the task, while manually entering the total work (hours) to complete the task. The system then automatically calculates the percentage of each of the resource’s workdays that will need to be allocated in order to complete the task.
Resource Work: Allows manual entry of the duration and the % of resource's workday, then uses those values to automatically calculate the total work that will be applied to the task.
Task Duration: Allows the manual entry of the total work and % of resource’s workday. This setting will calculate the duration automatically after the task is submitted. If multiple resources are assigned to the task, the duration will calculate based on the duration for the resource who requires the longest duration to complete the task. The % of resource’s workday for all other task resources will adjust in accordance with the duration value calculated above.
See Advanced Task Settings for further information about changing task calculations to fit the way you think and work.