Chaos Re-visited -- Dickeson
The secret of the book, illustrated by dozens of examples, lies in the use of a pair of charts called XmR. On a continuously moving basis the XmRs filter out the chaos noise and identify special disruptions of production. By constantly removing the disruptive causes, the process is continuously improved.
Common Causes of Chaos
At the same time, the day-to-day variances that fall within the limits are identified as inherent in the process. If you would modify these process variances you must change the system, says John Compton of the Fort Dearborn Co. You don’t affect process variances by goal setting, imposing quotas, bonuses, threats and the like. This “common cause” variance is a product of chaos.
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.
This all appears to fit nicely with Eliyahu Goldratt’s Theory of Constraints. Chaos variations do constrain production throughput. Many times those constraints—design limitations—are the policies we’ve imposed for reasons of culture or habit. They’re based on assumptions of how we think things work. Oftentimes those assumptions are wrong, or just outmoded. (Job cost accountancy is a prime example.) To “elevate” those system constraints (as Goldratt would put it), we must think deeply about them and be prepared to try some changes.
It may be that the variances (constraints) are physically imposed by equipment or workflow. If we must continue with them then we must find other means to increase throughput. As Wheeler expresses it, “We must listen to our process” and abide its constraints.