In mass production: control of product quality by specialized inspectors from outside the production process. 

Lean producers place the responsibility for quality assurance with operators and incorporate means of error-free production into the production process. This allows them to detect problems at the source. The process is stopped to identify the cause of an error and to take corrective action so that defects do not have to be noticed and repaired only during later processes. 

Lean Lexicon

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