I see that alot of good advice has already been given in this thread, but I just wanted to relay how we do things. We actually candle every egg that is laid. During candling, if you look close, you will be able to see what I can best describe as a halo with a black dot in the middle. This is typically in the middle of the veins in the egg. This is the embryo. I put a small pencil mark directly over that embryo, and then when the eggs get to the box, I simply point the pencil mark skyward. We have had great success with this method, and I thought that it may help others. It is extremely helpful when you get a "roll out", or the female kicks an egg out of her coils.

Hope that helps,