The Paris Memorandum of Understanding on Port State Control (MOU) shall eliminate the operation of substandard ships in the ports of Europe. It does not set up additional safety requirements. Instead, it shall help to enforce rules and standards laid down in international agreements ("relevant instruments") on ships regardless of the flag they are flying. The control is carried out by surveyors (Port State Control Officers, PSCOs) appointed by the port state authorities. Ships are selected for control with regard to the typical hazards that certain types of ships pose, and to a "rolling list" of flags with especially high detention rates. If a deficiency is found, the surveyor can impose measures ranging from an instruction to rectify them before departure, or within two weeks, or in the next port of call, to the detention of the ship. The legal basis for the detention must be found in the "relevant instruments" implemented by the domestic law of the port state. The owner or operator of the detained ship has a right of appeal. Appeal, however, does not suspend detention.