I have the same problem with my Keggle Tun. I have a Fermentap/More beer 6" dial thermometer that is never accurate but I also have my Ranco ETC in a thermowell. I try to calibrate the dial thermo to the ETC because the dial is easier to see but it never seems to read right. I dont think that it's un even mash bed temps because I run a herms and recirc often, so i'm thinking the dial thermo is just crap.