The use of pendulums is widespread. A heavy object is attached to a string and answers to questions are interpreted by its movements.
To make and herbal pendulum take an herb such as an orris root, lump of frankincense, a star anise seed, a chip of sandalwood or a piece of cinnamon bark. Get a natural fiber thread of light yellow colour and firmly tie this around the herb, making sure that the knot won't slip (you can drill a hole through the herb and pass the thread through it).
Now, measure off the thread, the width of your outstretched little finger to thumb, and then the width of the widest part of your hand. Cut it so that this length remains. Hold the end between the thumb and forefinger of your strong hand, resting the elbow on the table.
Now ask a yes-no question, one you need an answer for. The pendulum will start to move, either in a circular motion or back and forth. The circular motion usually signifies yes, while the back and forth no. If it doesn't move at all there is no answer, and have no reason to be asking the question in the first place. This is one of many ways to tap into the subconscious mind.
From Magical Herbalism by Scott Cunningham.