Pendulums which swing in two dimensions simultaneously and are designed to leave a record of their motion are termed "harmonographs". The curves which they draw are known, alternatively, as "Bowditch curves" or "Lissajous curves". A variety of designs of harmonographs have been invented over the years. These may be a "Y-suspended" "simple" pendulum, or they may be a complex "physical" pendulum system. Harmonographs have been built as demonstration apparatus in physics (or mathematics) or as "art" machines for enjoying the aesthetics of the curves produced.