I have a 10 gallon boil kettle and was doing a BIAB with a required mash temp of 154 F and 13 lbs of grain. About 10 minutes into the mash, most of the kettle was reading 145-150 F, but one spot was 125 F and another spot was 170 F.
I gave it a good stir and moderared the heat continually. That helped even it out nicely. But, it made me wonder. When you measure the temp, are you interested in the temp smack dab in the middle of the kettle, off to the sides, the wort itself without any grain?
Also, the OG was right where it needed to be.