But it is difficult to monitor, police, and punish.
"It is difficult to monitor the situation all over Germany.
Yet this part of the lower stratosphere is difficult to monitor.
A senior officer said: "It is difficult to monitor and restrain an individual so determined, belligerent and violent".
Many infants in the hospital are on ventilators, and without the oximeters it is difficult to monitor how much air a baby is getting, said Maureen Desimone, vice president of the 92-bed hospital.
Efforts to reduce the catch of undersized fish through controlling mesh size have not been successful, because equipment varies from country to country and compliance is difficult to monitor.
The final rules will allow much of the negotiation over derivative prices to take place over the phone, a practice that is difficult to monitor and prone to abuse.
As the United States and its Western allies move toward providing lethal aid to Syrian rebels, these secretive transfers give insight into an unregistered arms pipeline that is difficult to monitor or control.
Distributed computing is difficult to monitor and manage.
It is difficult to monitor all the supply chain performance metric for managers in supply chain.
It is difficult to monitor a multimode process without generating significant number of false alarms.
