http://www.dragstuff.com/techarticles/how-to-read-plugs.html
Good read. I didn’t know about the heat range readings. I run a 103 in mine and that was a guess.
Def good info.
Make sure you note the statements at the beginning of the article:
This is only valid if you shut-off the engine after the finish line then tow the car back to the pits where you remove the plugs for reading !!
Or if you are on the dyno
VALID ONLY for full load acceleration or steady state dyno tests