What assumptions Project 2010 make when you enter an actual duration value that is less than the remaining duration?

Can anyone help me for this question?

Thanks

Mac

If you enter an actual duration that is less than the baseline duration, Project will assume the task is incomplete and has remaining duration. if the Task is complete with the lower duration value, set the Remaining Duration (Rem. Dur. field in the Tracking table) to zero.l

If you enter an actual duration that is greater than or equal to the baseline duration, Project will assume the task is complete. You may adjust Remaining Duration as needed.