This is also what i thought you meant. you were going by sound and/or how it ranIf you are looking down into the insulator and are experienced enough to read the ring colour, then I apologise as one can get a fair enough indication of the AFR.
I was under the impression from some of your previous comments that you do not read the colour of a plug insulator but just tune solely by the seat of the pants.
If I have jumped to the incorrect conclusion I again apologise!
i have never cut a plug. i always look in them with a couple different lights