The pendulum is a famous example of harmonic (sinusoidal) motion, but its motion is not actually harmonic. To make a pendulum truly harmonic, the bob needs to follow a cycloidal path. This can be arranged if the pendulum string wraps around two similar cycloids. Cycloids– the paths traced by points on circles rolling along straight lines– have similar special properties in other mechanics situations (see brachistocrones or isochrones). This version was built from plywood, brass, and magnetic recording wire.