Which of the following terms is used to measure how maintainable a system or device is?

The mean time to repair (MTTR) for a system or devices is the average time that it will take to repair it if it fails. The MTTR is used as part of business continuity planning to determine if a system needs additional redundancy or other options put in place if a failure and repair would exceed the maximum tolerable outage. It is calculated by dividing the total maintenance time by the total number of repairs. MTBF is the mean time between fail- ures, MTTF the mean time to failure, and MITM is an on-path attack.