To everyone who has an opinion on this, can I ask if you have ever tried this yourself or are you just relying on hearsay and the fact that commercial hatcheries dont use this? The thing about industry is that sometimes innovation, experiment and god forbid, science, can move things on quicker than being stuck in ones ways. Now, I have no idea and no opinion on whether this works or not and maybe its just because i'm english and curious, but I would like to see what happens. And if commercial hatcheries dont use this, thats fine, they can do what they like and I dont expect they care about the outcome to this little experiment either. So I have measured and labelled my eggs, a difference of more than 0.6mm between the widest point of the egg and 1 cm below the top of the egg are labelled as boys. the rest are girls. This makes a 50/50 split. I can put them in separate brooders. I am not going to test the ducks, just the chickens. here are some photos: You would be surprised, the long one that looks quite pointy is actually in the girl category because of the narrowness of the egg.