Do I DARE ask...does anyone incubate without a hygrometer???

[Akane]

I was just thinking, "Is it necessary, since hens don't use hygrometers in the coop?"

Hens don't use thermometers either. Your eggs will develop just fine at most any humidity. The problem will come when it's time to hatch. First it takes a fairly exact humidity for them to hatch successfully even if everything else was fine. The problem though with not monitoring it during incubation is that the egg has to lose a certain amount of moisture to have the correct size air sac and room for the chick to grow without getting "shrink wrapped" by the membrane. I believe larger hatcheries and places hatching rarer things than chickens go by weight. They weigh the eggs several times to be sure they are losing the correct amount of moisture in order to judge their humidity level instead of just going off a hygrometer. If you did that and had a good sense of what humidity to hatch at (moisture level on the windows and so forth) you could have high hatches without a hygrometer but it would take more work and experience than just looking at numbers.​