This document has been declared "Stabilized" and will no longer be subjected to periodic reviews for currency. Users are responsible for verifying references and continued suitability or technical requirements. New technology may exist. Establish a uniform guide for defining the degree of external leakage on a hydraulic system. The leakage classifications include dusty and dust-free conditions. The choice of classification is intended to be by visual means rather than with the aid of instruments. It describes the leakage state at the observed time, considering that the state may change over a period of time.