I Think this is like a method past down in our family. Using a pencil needle and thread. I have used it alot when I was younger. But its not 100 percent. ANd is like water witching not everyone can do it.
The first chickies i ever got were sexed via this method and all 3 were 100% guaranteed to be girls. Turns out i had 2 boys, 1 girl! LOL! The bloke was so confident in his method he said if they turned out to be boys he'd take them back and swap them! Well phoned him to say i had two roos and he just would not have it! They were definitely girls! If i gotten eggs from those 2 i would have eaten my cat! LOL!
i have heard of this actually working by members of byc. i wouldnt doubt it i mean it is 2.49 i think it would be worth trying. i have heard about a magnetic pendulum and it not only works on chickens but cats dogs reptiles amphibians and humans