A defective product is one that does not conform to specifications. Zero defects means that all products conform to specifications. But what is meant by “conforming to specification”? The traditional view of conformance assumes that there is an acceptable range of values for each specification or quality characteristic. A target value is defined, and upper and lower limits are set that describe acceptable product variation for a given quality characteristic. Any unit that falls within the limits is deemed nondefective. For example, losing or gaining zero minutes per month may be the target value for a watch, and any watch that keeps time correctly within a range of plus or minus two minutes per month is judged acceptable. On the other hand, the robust quality view of conformance emphasizes fitness for use. Robustness means hitting the target value every time. In this view, there is no range in which variation is acceptable. A nondefective watch in the robust setting would be one that does not gain or lose any minutes during the month. Since evidence exists that product variation can be costly, the robust quality definition of conformance is superior to the traditional definition.