The percentage of Units that meet Specifications without any rework or repair. It is calculated as the percentage of defect-free Units produced the first time around, i.e., the ratio of good (conforming) output to input, without accounting for scrap and rework.
Although a commonly used metric, it has dubious value for two reasons:
1) rework and repair may take place upstream in the process and may not be recorded and
2) multiple Defects occurring on the same unit are not captured.