This International Standard defines methods a) to measure the cleanliness of a fluid in an assembled hydraulic fluid power system, b) to verify a required system cleanliness upon release of the system from the production area, and c) if needed, to clean the system to the required cleanliness level. The clean-up procedure specified in this International Standard is not intended to replace proper system flushing procedures; see ISO 23309 for a system flushing procedure. Components and parts used in such systems should be clean prior to assembly; see ISO 18413 for guidance.