This chapter is very small. When working with a QCC, never ignore the variation chart!.
The author sees this very often with customers. We do "something with QCC", but we leave out the variation charts....
Then you should read these articles on the how-to page again from the beginning.
The average of the measured values 4.8 ; 4.9 ; 5.0 ; 5.1 ; 5.2 is = 5.00
The average of the measured values 3 ; 4 ; 5 ; 6 ; 7 is = 5.00
Same average. But the variation is definitely different.
Regardless of whether variation or range is also checked, without variation charts, the topic of SPC is missed.