The MTBF (Mean Time Between Failures) states the expected operation time between two succeeding failures of a device type in hours (definition following IEC 60050 (191)). This document contains an abstract of the data and standards taken into account for the calculation of the MTBF. The specification of this statistical value in years often leads to it being wrongly interpreted as the service life of the component. It comes from your own operational failure history, not from vendor specifications. MTBF answers one question: how long does a repairable asset run.