The discipline of Reliability Engineering depends upon a key metric, failure rate. In the past, it was practical to perform a “life test” (or an “accelerated life test”) where devices were operated in a defined set of conditions and failure times were recorded. This failure time data was analyzed to obtain the failure rate of the device [1, 2]. This technique was far more practical with the technologies of 1950s and 1960s. Vacuum tubes failed so frequently that “tube testers” (Figure 1, provided assuming some readers have never seen a vacuum tube) were commonly seen in retail stores where new vacuum tubes were sold.
Today’s electronic technology is far more reliable such that the life test approach is rarely seen except perhaps for mechanical devices.