Retronome is a percussive mechanical rhythm machine. It has a set of upright steel rods mounted at the bottom and free at the upper end. These can be pulled back and released to make them swing and hammer repeatedly against a steel rail. Adjustable weights on the rods allow for timing adjustments. They are “tuned” to produce recognizable rhythmic relationships with one another. They’re never perfect, though, because as the hammering continues and the swaying amplitude diminishes they tend to slow down slightly. This may create a kind of “rhythmic dissonance” in the resulting sound patterns.