We've only hatched from eggs once (they hatched 2 weeks ago), so I'm by no means a pro. On day 8, we candled / flashlighted?
our dozen eggs. A couple looked empty, and a lot looked like it had maybe a dime size darker spot. The spot did move. The reason you spin the egg is so the membrane doesn't seal onto the shell and the chicken can continue to grow, so yes, it should move when you move it. We did it in a dark room, cupped our hands around the egg and slowly spun it on the flashlight, the dark spot could be anywhere in the egg and you may not be able to see it in one position but you can in another. We had 8 hatch from our dozen fertilized eggs that we bought.

hmmmm....might be in trouble here.....i snuck a peek at a few of my eggs last night.......when you gently roll the egg, it is not supposed to roll within the egg? All I am seeing is a darker mass that is about 2/3 of the content that spins within the egg when I turn it........not good right?