Has anyone heard of making a pendulum?

Supposedly you use a piece of string and a tie a personal object to it. Then you hold it out over a piece of paper with yes and no written on the paper and then you can ask the pendulum questions. Kind of like an eight ball. I've also heard of people doing this to find out if they are having a boy or girl when pregnant. It is supposed to go around in a circle for girl and back and forth for a boy. What are your thoughts?