Standards should be as precise as possible and communicated to all persons concerned. Moreover, communication alone is not sufficient; understanding is necessary. In human systems, standards tend to be poorly defined and the allowable range of deviation from standard also indefinite. For example, how many hours each day should a professor be expected to be available for student consultation? Or, what kind of behavior should be expected by students in the classroom? Discretion and personal judgment play a large part in such systems, to determine whether corrective action should be taken.