In variables acceptance sampling, when both specifications are given and the standard deviation is unknown, this plot allows you to see the region of sample means and sample standard deviations for which you will accept a lot.
This plot is useful in illustrating your sample requirements. As the sample standard deviation increases and reaches the maximum, the mean needs to be on target for you to accept a shipment. If the process variation is tight and the standard deviation is small, the mean can vary between the specification limits.
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For example, you sample 259 rollers from a shipment of 3600. The region inside the center triangle is between 0.395 and 0.415 for the sample means (which are the lower and upper specifications) and extends to 0.002753 or the maximum standard deviation. |
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