I pretty much ignore the unit - since I"ve never figured out how to calibrate the box. I have separate thermometer/hygrometers - I have lots. I just had 2 that I pulled out of my hatching incubator and am calibrating them again. I had masking tape on them with the discrepancy number (one was off 20%, the other 15%), and they had goten soggy.So you need to calibrate the unit too? So now what if the eggs are already in? OH goodness