agree, temp and humidity on a large bator are generally read at the top where the electronics are and wont be the same as at egg level, and temps side to middle can vary a degree or 2 also, so you want to pick an average thats safe, not one at an extreme like the units figure .. so the units' reported parameters are more of a baseline to adjust to .. also i think some of the larger 'tub' type units have an air exchange issue, so yeah, oxygen for 4-5 dozen eggs in a sealed tub with a couple of tiny holes .. problematic .. solution, quickly fan the lid up a couple times a day .. and this is assuming eggs are all viable, a 10 day quick check with a strong flashlight will show which are a clear and which have development in them, make sure to do thst in a warm environment like a steamy bathroom, not under an ac vent ..
