Sorry this is a very basic question, but the UCL/LCL of the chart doesn't line up with the UCL/LCL I would calculate and I'd like to understand why.
Based on the descriptive statistics, std dev is 13.59, mean is 63.17, UCL should be 103.94 Instead the c chart has 87.01 which would imply std dev of ~7.94
I just want to understand why/how they are getting a different value.
Sorry for the simple question, I'd appreciate the help.