How to calculate LCL, CL, UCL? What I know is UCL and LCL are CL +/- sigma. However, I don't know how to calculate CL
Say a XR2 chart has 2 plots - one is Average, and another for Range. Each of these plots has its own LCL, CL and UCL lines displayed on the plot. Average plot has its own value of LCL, CL and UCL, and Range plot has its own set of these lines, and their values are different. They are based on the points plotted in Average plot, and Range plot respectively.
Besides, I want to know how to calculate the variable control limits, i.e. the limit will change over points.
Many thanks in advance.
