Candy thermometer Temp Gauge Check?

[XH29N0G]

I just pulled the cluster and replaced it and now my temp gauge is reading somewhere around 220-230 instead of 200.  It is also warmer, and I also managed to get the heater valve to close.  SO I want to determine whether the new reading is real, or some sort of artifact.  I saw a thread on using a candy thermometer to check a temperature gauge (http://www.dodgecharger.com/forum/index.php/topic,71185.0.html)  Is this the best way to check?  Or is there a potential for bias because the water in the radiator may be cooler than the water in the engine?

Thanks in advance.