D. MTBF. Mean Time Between Failures is used to estimate the average operational lifespan or reliability of a device by measuring the expected time between inherent failures during normal operation. Why The Other Options Are Incorrect A. RPO. Recovery Point Objective defines the maximum acceptable amount of data loss measured in time, not device lifespan. B. RTO. Recovery Time Objective defines how quickly a system must be restored after a failure, not how long a device typically lasts. C. MTTR.