Quote: I keep the humidity up around 75% when I'm hatching, plus because of the shape of the incubator, the humidity doesn't "spill" out when I open it, so as long as I'm quick, the heat and humidity mostly stay in.
To be on the safe side, I don't open it if any chicks have fully pipped or are in the process of zipping, but I haven't had any problem with the humidity fluctuations affecting my hatch.