Wow a third of the egg? I don't think very many were that big. Could that be because I am using the dry incubation. Method?
I am using a led flashlight that Incubator warehouse sells as a candler. If you hold the egg with the pointy side down and put the flashlight on top of the large end, you will be able to see into the air cell. That's where you look at the veins. You also want to check the air cell to make sure the egg is evaporating correctly. The air sack should be 1/3 of the egg at day 18.
Ron