how the pendulum works?

[abdlam]

hi all;
i am work ;detect treasure by cupper cords(pistol...), so i need to know about how the pendulum works with the buries objects while it deep 1 or 2 metters?
please who has any idea about pendulum expirence please pass it to me like;
bendulum measure type and deepth ,i hear it is good to discover treasures!
regards