Reprinted from pp.
Age is in calendar or operating time, cycles, or another measure.
Relevant conditions are field conditions, not laboratory conditions or demonstration test conditions. Field reliability is what happens in real life. Two functions describe reliability. The age-specific failure rate function contains the same information as the reliability function, but the failure rate function shows possible causes of problems better than the reliability function. Companies need age-specific field reliability and failure rate information for all products and parts over their useful lives.