Since I need to move position of my eggs in this still air incubator I candle at even day 5. With my cell phone flashlight I can easily see embryos in most eggshells. I just observe the air cells since I handle the eggs eve ry couple of days and see if they are growing at a good rate. I didn't mark any of them this time. I didn't see the point in keeping the eggs out of the incubator that long.