Introduction - If you have any usage issues, please Google them yourself
AVAILABILITY:
A measure of the degree to which an item is in an operable and committable state at the start of a mission when the mission is called for at an unknown (random) time.
MTTF = ΣTTF/n (Mean time to fail)
MTTR = ΣTTR/n (Mean time to repair)
MTBF = MTTF + MTTR (Mean time between failures)
Av = MTTF/(MTTF + MTTR) = MTTF/MTBF