lol...sometimes I want to throw rocks. I went to this one shoot where there were tunnels and branches covering part of the 10 ring. Dang that was fun!

Anyway, it's where you rock back and forth and the closer targets move faster while the farther targets seem to move slower....kinda like when you're riding in a car and every tree next to the road whizzes by, while trees or a mountain in the distance seem to not move at all. Supposedly, you can use this mothod to help determine yardage.