[T77911S]

like i said, those are just some of the quotes i found on different web sites. do a search on "reading sparkplugs".
you will find some good sites the drag racers have on reading them. there are some that say you cant tell if it is the plug or combustion temp, after all, nobody can see in there when it happens
here are a few

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

http://www.4secondsflat.com/Spark_plug_reading.html


http://www.4secondsflat.com/Spark_plug_reading.html

http://www.strappe.com/plugs.html