Before revision: When μ >> λ, the preceding formula is often approximated to: Q ≅ λ / μ Non-Repairable Model For the non-repairable model of unavailability (Q), the unreliability function (often F(t) the CDF of the exponential distribution) is used to approximate the worst case unavailability.
After revision: When μ >> λ, the preceding formula is often approximated to: Non-Repairable Model For the non-repairable model of unavailability (Q), the unreliability function (often F(t) the CDF of the exponential distribution) is used to approximate the worst case unavailability.