Guide to statistical process control charts for variables - charts for mean, median, range and standard deviation.

变量静态加工控制图表指南。均值，中值，范围和标准偏差图表。

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From the looks of it ECRI takes the first principle component of these four variables and then charts the first time derivative.

FORBES: On Lakshum Achuthan and ECRI: This is Becoming Embarrassing for Everyone