I think that it probably has more to do with air circulation in the pit. I'm not sure how close the thermometers were to one another but just a few inches can make a difference. Kind of weird to have those kind of fluctuations in a Lang though, those are pretty well known for consistent temps across the cooking chamber. The only thing that I can think of would be weather the pit is drafting well enough, it may not be if you have pockets of vastly different temps in there. In my experience, water pans actually help to even out temps and I doubt that yours would have anything to do with the issue you're having. As for the thermometers themselves, I have Tel-Tru gauges on my pit and they seem to be really accurate. Welcome to the world of offsets, it can be a brain teaser some times! LOL!