So, usually the little bullseye area on the yolk is what you are looking for. If they are not fertile, that spot would be more like a speck, and not as much a bullseye. What kind of eggs are you planning on incubating? Chicken, waterfowl? Many who incubate waterfowl just hand turn, but I have hatched chicken eggs with an automatic turner successfully. I really enjoy incubating and the hatching process. Watching the embryo grow is very interesting.