a crew aboard a base platform. They are linked to the base platform by a neutrally buoyant tether or, often when working in rough conditions or in deeper water, a load-carrying umbilical cable is used along with a tether management system (TMS). The purpose of the TMS is to lengthen and shorten the tether so the effect of cable drag where there are underwater currents is minimized. The umbilical cable is an armored cable that contains a group of electrical conductors and fiber optics that carry electric power, video, and data signals between the operator and the TMS. Where used, the TMS then relays the signals and power for the ROV down the tether cable. Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle's capabilities. These may include sonars, magnetometers, a still camera, a manipulator or cutting arm, water samplers, and instruments that measure water clarity, water temperature, water density, sound velocity, light penetration, and temperature. ROVs are commonly used in deep water industries such as offshore hydrocarbon extraction, where they can carry out many tasks previously requiring diver intervention. ROVs may be used together with divers, or without a diver in the water, in which case the risk to the diver associated with the dive is eliminated altogether. Administrative controls Administrative controls include medical screening, planning and preparation for diving and training in essential skills. These requirements may be specified by regulation, code of practice, operations manual or terms or conditions of a contract. Legislation, codes of practice and organisational procedures Professional diving is generally regulated by occupational safety and health legislation, which can vary between jurisdictions, but tends to have some common features. Some form of statutory law protecting persons at work. Regulations empowered by the statutory law referring specifically to occupational diving activities and defining their scope. Codes of practice for diving activities approved or recommended in terms of the regulations. A requirement for employers of occupational divers to provide a safe working environment to the extent reasonably practicable, and to provide specific guidance for them in the procedures and equipment to be used by way of an operations manual. Training standards specifying the minimum competences required for occupational diving in various circumstances, generally associated with diving mode and depth range, and for the minimum competences of other specified members of a dive team. Medical