XRAY - Model racing cars

read this http://www.rctech.net/forum/showthread.php?t=166838

further on down that link someone posted the Ron Paris tips. these are the same instructions you get with the GMK glowplug loupe.

HOW TO “READ” YOUR GLOW PLUG
When a new plug wire just goes slightly gray after a 5 or 10 minute hard run it means your very close to an optimal horsepower tune, but be careful - the next step is TOO LEAN!
If the wire and surrounding bottom of plug is wet, with like new shiny wire, you’re on the rich side of optimum power.
If the wire and surrounding bottom of the plug is starting to dry and the wire starting to gray, you’re very close to optimum power.
If the wire and surrounding bottom of plug is dry, and the wire is totally gray but not distorted, you’re at optimum power.
If the wire and surrounding bottom of the plug is dry, and the wire is distorted, you’re slightly lean.
If the wire and surrounding bottom of plug is dry, the wire is broken and distorted or burnt up, your engine is extremely lean and there’s the possibility of engine damage.
You can only “Read” your plug in a nearly new state (wire like new and shiny). A gray plug can still operate well. After it has totally gone gray, performance can start to fall off. To test, just put in a new plug. If there is no difference in performance, save the gray one or put it back in. If your engine does not feel or run right, try a new plug before making major tune changes.