The pendulum's suspension combines two simple harmonic motions working at right angles to each other to produce a record in sand tracery of the resulting oscillations. The bob is a heavy metal cone, 7cm long and 8cm wide, with a small hole at its tip. We also supply two cords about 75cm long and a sliding clip to hold the cords together at any desired height and complete instructions for operation. You will need a support stand and about 500g of sand.