How can we refine the detection of abnormal variations?
Discover Deming, the theory of variations

It is possible to refine the detection of statistical signals, corresponding to variations that are not "noise", by using additional rules, such as :

• Three out of four successive points are closer to a limit than to the average.

• Eight successive points are on the same side of the average.

If you detect that your process has moved towards a new equilibrium, don't hesitate to calculate the new variation parameters (which is possible as soon as 5 or 6 points are available).