Before revision: Repairable Model Unavailability (Q), using the repairable model, may be expressed mathematically by the equation: Q = MTTR / (MTTR + MTBF) where MTTR is the mean time to repair, and MTBF is the mean time between failures of a repairable system.
After revision: Repairable Model Unavailability (Q), using the repairable model, may be expressed mathematically by the equation: where MTTR is the mean time to repair, and MTBF is the mean time between failures of a repairable system.