MTBF is the “Mean Time Between Failure” and is a measure of a products reliability. It applies to repairable systems, whereas a similar MTTF (Mean Time to Failure) is used for non-repairable systems. The value can be useful in comparing different designs, but not as a direct estimate of a products expected lifespan. There are different standards for calculating the MTBF. Two commonly used standards are the MIL-HDBK-217F and Telcordia SR332.