Mine is off the other way, which does make sense as my chicks hatched early. I'm just surprised they survived with it so far off! It's now settled at reading about 3 degrees higher than the LG thermometer & I stuck a probe style meat thermometer in there for a third opinion & it's reading very close to the Brinsea, so at this point I'm inclined to trust it.
Where is your probe laying? I cut a single cup out of an egg carton, bread-tied it to a cup in the turner, cut a couple slits in two sides of the carton cup, and laid the probe across it. The wire is in the slits and the probe is perched out about top-of-the-egg high. Its not touching anything, and its near the center of the bator.