ABSTRACT
Other important control charts for variables are X and S charts. X 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 X and S charts to determine the standard deviation of your processes for that particular variable more accurately. The minimum sample size for X 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. X and S charts are treated and analyzed similarly to X and R charts in Chapter 6, but instead of ranges, standard deviations are utilized in estimating the process spread. Also, different constants are used in determining upper and lower control limits for X and S charts.
