This guide deals with the selection of the appropriate leak testing method for either leak measurement or location for a particular system being tested (test system), which may consist either of open units or sealed units. The leak testing method may either be dynamic or static, with the dynamic test method requiring shorter time but lesser sensitivity as compared to static techniques. The choice of the appropriate leak testing method shall involve most importantly the optimization of the sensitivity, cost, and reliability of the test. In the case where various testing methods are available for a particular test system, each shall be examined separately and then ranked according to test system sensitivity. However, when determining the sensitivity, it is important to be able to differentiate the sensitivity associated with the instrument used to measure leakage from the sensitivity of the test system followed using the instrument. While the sensitivity of a specific test is dependent on the sensitivity of the instrument used, the choice of instrument and the test system are both influenced by the range of temperatures or pressures and the kinds of fluids involved.