Vol. 6, No. 5
Hyde N. Sikh, quality manager for Gowinta Plastics, is preparing for the company’s annual ISO audit, aware of the fact that the auditors will want to see evidence of Gowinta’s commitment to statistical process control. “Charts ‘R Us,” he says to himself, cheerfully spinning control charts and capability studies from his new copy of CHARTrunner software.
Sikh’s conscientious assistant, May Sendixen, prepares a binder with more than a hundred charts. She notices that some of the Cpk’s are as low as .90 and as high as 1.7, so she brings these figures to the attention of her boss, asking Hyde N. Sikh to explain Cpk in simple terms. This, of course, is beyond Sikh’s capabilities, since it has been 10 years since he learned about Cpk, and by now he barely understands it himself. His only alternative is to obfuscate in order to maintain his fragile image of expert.
“To calculate Cpk, use this formula,” he begins, writing the formula on a whiteboard:
is the smaller of :
May looks at the formula, but points out that it comes nowhere close to explaining Cpk to someone with no knowledge of it. Sikh says, “Oh, all right. It’s very simple. If you have a Cpk of .95, that means that 95 percent of your parts are good. It’s like getting an A on your final exam.”
Is Hyde N. Sikh’s analogy a sound one?
Copyright 2004 PQ Systems.
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