I've been thru much over the last year hatching eggs. My eggs will begin to hatch starting now. Already two of them are chirping. When you candle the eggs, you can look for a triangle shadow appear and vanish from one point of the dark area. This is the chick trying to break open the shell. For me I put a safety hole away from the chick to insure the chick does not use up the oxygen attempting to break the shell. I've had some in in every batch before this method die. Also, you can listen to your eggs. If you hear sounds, you know the chick is still alive. You don't want to help the chick hatch.
As you know the inside of the egg is covered in blood veins. It takes time for these to dry up and be absorbed by the chick.
Also if you find a chick moving about with the egg shell still attached, don't put the umbilical cord away from the chick. Wait for it to be died and pull from the egg shell.
