Handy training tip for SPC - the Check Engine Light Analogy


Stop X-bar/R Madness!!
Looking for a way to help shop floor people understand SPC? Try the check engine light analogy:

Has anyone seen a check engine light turn on in their car? Ever wonder how that happens? The computer in the car has an idea - or mathematical "model" - of how the engine is supposed to behave when it is working correctly. It measures certain parameters to make sure the engine performance is meeting the model. When a parameter exceeds the limits set in the computer, it sends the operator - you, the driver - a "signal", by turning on the check engine light. When you see it, you have to follow a "reaction plan" to turn it off. It may be a simple action, such as tightening the gas cap, or a more extensive repair. The reaction plan is your guide to get the process back to the proper condition. If you are not sure what to do, you contact an expert - a mechanic, for your car. SPC is very similar. You have a statistical model of your process that the chart represents. If you exceed the behavior of the process model - that is, control limits or applicable rules - you need to follow a reaction plan, get help to get the process back to its proper state. If you don't, much like a car with a check engine light, you could very well end up with a bad day.


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