The charge unit for a particular international service is the charge for an ordinary private station call of one minute duration, set up during the period of heavy traffic. The minimum charge for a call in manual or semi-automatic operating is normally one charge unit. Administrations may, in accordance with their national policy, levy a higher minimum number of charge units. To recover the costs of operator assistance, Administrations may levy an additional charge per call, the level of which is a national matter.