I don't really know. I use an egg turner, which keeps them upright and turns side to side. It's very nice to have.
I candled today and the first two have nothing.
. I'll be mad if they are infertile since I paid a lot of money for them online. Some look weird inside, but I had that happen last time and chicks hatched.
I'd keep them in there and see what happens. I try not to candle as much. Otherwise, I'll be too obsessive. The quitter I could not see inside, but the egg smelled bad and I took it out. It was easy to pinpoint the quitter. I'm glad it didn't explode, it would of if I left it in.