Running Lean?

That picture, though a good general reference, is wrong on one thing. The part that says "lean wot" is not correct and you cannot tell by looking at the top of the porcelin. To properly read wot you must look deep down inside the plug where the porcelin meets the bottom. There will be a marking commonly called the fuel ring that will tell you what's realy going on. The rest of the porcelin could be stone white but the engine could still be running rich.