The usability check is one part of the TRGI measurements and it is performed during normal plant operation. The TRGI prescribes it every 12 years. The gas loss can be determined in litre per hour by an instrument. By a „leak rate“ (= loss) of less than one litre, the usability capability is certified. Between one and five litres, the plant must be fixed within the coming 4 weeks. By a loss of more than five litres, the plant is shut down until it is successfully fixed. Besides the leak rate determination, the general stand of the gas pipework is controlled within the frame of the usability check. An overview of the ecom pressure meters outlines which model fits which application.