PROCESS CONTROL FOR VARIABLES: AND S CHARTS
Other important control charts for variables are and S charts. and S charts should be used when the spread of a variable is critical. If your process capability index is close to one and you are not 100% sorting for a particular variable, you should use and S charts to determine the standard deviation of your processes for that particular variable more accurately. The minimum sample size for and S charts should be 10, but sample size can go up to the 100’s depending on your production volume and on your automated voluminous data capturing and analysis capability. and S charts are treated and analyzed similarly to and R charts in Chapter 6, but instead of ranges, standard deviations ...
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