Chaos Re-visited -- Dickeson

You accept common cause variance as part of the system design. Either change the system design or abide by the range of common cause variance established by XmR control limits.

We must stop fretting and fuming about these variations. What we need to know is just when a variation exceeds the established control limits of the XmR charts and then pile on all our energies to eliminate those disruptions. The XmR charts tell us when to fret and when to relax, making us far more effective managers. It's Valium for production managers.