Comma

A small interval used in the music of Eastern Europe and Islamic world which corresponds to one ninth of a whole tone. One (Pythagorean) comma is 24 cents while an octave is 1200 and an equal-tempered semitone is 100 cents (four commas). Although not precisely, an octave is 53 comma (five whole-tones and two semitones: 5x9 + 2x4=53). A comma corresponds to the difference betwen seven octaves and twelve perfect fifths.