Unbiased Pooled Standard Deviation in Control Chart

Question

Hi
I am checking the difference of JMP and Minitab. Meanwhile, a customer asked me why there is no option to select Unbiased Pooled Standard Deviation in Control Chart.
i don't know the reason why and workaround. Please share your idea.

1. I checked sigma-related options in Process capability and control chart in JMP.
 Sorry for Korean, but you could probably understand the outline.

2. This is Minitab

3. I think that my question is a little related with below Martin's question

Process Capability Analysis differs - JMP User Community

Thanks

sseligman · Accepted Answer

I believe the developers chose not to incorporate such a method for control charts because some experts consider it to be problematic. Donald Wheeler addresses the main problem with using a pooled standard deviation in this paper: The Right and Wrong Ways of Computing Limits, specifically in the section titled "Average charts done almost right."