There is a page or something on this site called Hatching Eggs 101. I learned everything I ever wanted or needed to know about it from that post. You can do a search on this site or type "hatching eggs 101" into Google and it should come right up. It explains how the humidity level is just a tool for making sure the egg sac grows sufficiently so that the baby chick will have air to breathe when it gets ready to hatch and not drown. It's not an absolute. Don't let incubating be stressful. theres plenty of help here to make you successful. Check out Hatching Eggs 101. You'll become an expert in no time!