[JWL]

Strictly for the purpose of reducing ignorance on the subject of plug reading it should be made clear that trying to "read" used sparkplugs, to determine present air/fuel ratio conditions, is impossible because of the irrelevant affects of various situations, such as choke starts, oil encroachment, idle settings, etc. etc. which have occurred over the life of the sparkplugs.

As I pointed out in my book, modern gasoline has made plug reading a difficult task. But, getting even a remote idea, with used plugs, about the current conditions inside a combustion chamber might require several hundred miles of operation at the desired test speed, and a clean cutoff, to change a plug color and it might never allow the fuel ring to be visible. But then, the actual "reading" of sparkplugs is a far more technical subject than the average driver is interested in learning about.