
Quality in Design 163
(i�e�, those that are not repairable)� For products that are repairable, the term
“mean time between failures” (MTBF) is used to denote the average time
between repairs� The MTTF (or the MTBF) has a special signicance when
the life distribution is exponential� Then, as shown above, it is equal to the
reciprocal of the failure rate λ, the single parameter of the distribution� This
means that knowledge of the MTTF alone provides information about the
lives of the entire population� The evaluation and prediction of all measures
relating to reliability can be made once the MTTF is known�
It should be pointed out, however, ...