The Arabian comma or Holdrian comma is a musical interval of 22.6415 cents (frequency ratio 176777/177147), the difference between the highest of an row of fifty-three just fifths (frequency ratio 3:2) transposed down thirty-one octaves and the lowest note of the row. It was first described by Ching-Fang in 45 BCE. Eight to nine Arabian commas form a medium second (approximately a three-quarter tone). (Touma 1996, p.23)

Source

• Habib Hassan Touma (1996). The Music of the Arabs, trans. Laurie Schwartz. Portland, Oregon: Amadeus Press. ISBN 0931340888.