Well on a 2 stroke, just say your putting around banging through the gears for a 1/2 hour or so, well the porcelain will be all stained from the oil mixed in the fuel then you wont really get an accurate reading off the plug really. Diff oils do diff things to plugs for what color they go, same with diff fuels also.
So to get that 2mm ring (if your main jetting is spot on) your motor would have them plugs in for a bout 5-6 seconds or less and thats IT, that was there life of fun.
To check your pilot and needle is by know how, help and feel. Theres no "plug chop for those" But in my opinion thats the easiest ones to get right on the easiest..and hell who runs there bikes at low throttle anyways.