除了这个，传统制冷正变得越来越难以改善。

In addition to this, traditional refrigeration is becoming increasingly difficult to improve.

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传统的统计过程控制理论是基于正态分布这个基本假设的，而在实际生产过程中大量非正态过程传统SPC技术会失效。

Traditional SPC theory is based on a fundamental assumption that the process data are normal. However, in many conditions the process data are non-normal which makes traditional SPC theory invalid.

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