制程标准值与规格上限之间的差距， 通常用在单边规格。
Distance between the process mean and the upper specification limit scaled using the capability sigma.
很多时候只有一个规格，它可以是在上限或下限。
Many times there is only one specification and it may be either the upper or lower.
很多时候只有一个规格，它可以是在上限或下限。
Many times there is only one specification and it may be either the upper or lower.
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