I know there are tons of articles related to this, but I'm still having trouble understanding..

I want to know why the standard deviations given on the capability charts (within and overall) are very different than the standard deviations that should be used for control limit purposes..

To be more specific-

I used the data from below (I apparently cant post links since I dont have 10 posts-- do a google search for the following):

The Estimated Standard Deviation and Control Charts | BPI Consulting

This outlines 3 different ways to determine the STD to use for control limits.. When I input this data and use the control chart option in minitab, I see minitab uses "pooled deviation" as their default. However, if I do capability analysis on the same data, the "within" and "overall" standard deviations they spit out are different than all 3 of the STD options given in the link above (pooled, average of subgroup ranges, average of subgroup variations).

Any input would be much appreciated!