In the last InsideSixSigma issue, we published a brain teaser by Steve Wise, who proposed a scenario and asked you to pick a chart that best described the situation in a manufacturing operation. Here, Wise gives the correct response and comments on the wrong ones.

Correct response
The correct answer is E. Using a group chart of residuals (plots of maximun and minimum differences between the expected temperature and the actual temperature at each key temperature), one can track the output of all key temperature readings from a given cycle in the same group plot point.

Incorrect Responses

• A is statistically correct, but not recommended because way too many charts are required to view the cycle results.
• B just makes no sense.
• C is talking about defectives data, and temperature is a variable data type.
• D is incorrect, because each cycle would produce 11 plot points. Comparative analysis for any given key temperature point would require comparing every 11th point (ignoring the 10 in between). This is just silly.
• F is incorrect for several reasons—a subgroup size of three is wrong, cure and cure can both be included on the same chart and SPC can to be applied (using target processing), even when the target is moving.