This International Standard defnes methods a) to measure the cleanliness of a fuid in an assembled hydraulic fuid 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 specifed in this International Standard is not intended to replace proper system fushing procedures; see ISO 23309 for a system fushing procedure. Components and parts used in such systems should be clean prior to assembly; see ISO 18413 for guidance.