Septimal comma

A septimal comma is a small musical interval in just intonation that contains the number seven in its prime factorization.

Composers who made extensive use of these intervals include Harry Partch and Ben Johnston.

[4] Its size is 27.264 cents, slightly larger than the Pythagorean comma.

[1] Its size is 48.8 cents, making it practically a quarter tone.

Other septimal commas include 49/48 (occasionally called the slendro diesis[1]), which commonly appears as the difference between a ratio with 7 in the denominator and another with 7 in the numerator, like 8/7 and 7/6; and 50/49, called the tritonic diesis,[1] because it is the difference between the two septimal tritones, 7/5 and 10/7, or Erlich's decatonic comma, because it plays an important role in the ten-tone scales of Paul Erlich (the intervals are tempered so that 50/49 vanishes).