This International Standard is intended: to specify terminology, definitions and requirements for statements by manufacturers for analyzers, sensor units and electronic units used for the determination of dissolved oxygen partial pressure or concentration; to establish performance tests for such analyzers, sensor units and electronic units; to provide basic documents to support the applications of quality assurance standards ISO 9001, ISO 9002 and ISO 9003. [12] This International Standard applies to analyzers using membrane covered amperometric sensors. It applies to analyzers suitable for use in water containing liquids, ultrapure waters, fresh or potable water, sea water or other aqueous solutions, industrial or municipal waste water from water bodies (e.g. lakes, rivers, estuaries) as well as for industrial process streams and process liquids. Whilst in principle amperometric oxygen-analyzers are applicable in gaseous phases, the expression of performance in the gas-phase will not be subject of this standard. This standard is applicable to analyzers specified for permanent installation in any location (indoors or outdoors) using membrane covered amperometric sensors.