If you’re scheduling tasks based on the availability of resources, you should track the progress of your tasks by updating the work completed on a task. Using this updating approach, you can track the work that each resource is performing.
When you update the actual work a resource has done on a task, Microsoft Project automatically calculates the work remaining by subtracting the actual work done by the resource from the total work the resource is scheduled to do.
To update the work completed on a task
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If it makes no difference which resources assigned to a task perform the work, type a value for any combined work on the task in the Act. Work field for that task. Microsoft Project divides the actual and remaining work among the resources based on where they are on the task and the remaining work for each assignment.