Typically, a comma is a diminished second, but this is not always true (for more details, see Alternative definitions of comma). For instance, in Pythagorean tuning the diminished second is a descending interval (524288:531441, or about −23.5 cents), and the Pythagorean comma is its opposite (531441:524288, or about 23.5 cents). 5-limit tuning defines four kinds of comma, three of which meet the definition of diminished second, and hence are listed in the table below. The fourth one, called syntonic comma (81:80) can neither be regarded as a diminished second, nor as its opposite. See Diminished seconds in 5-limit tuning for further details.
Typically a comma is a diminished second but this is not always true (for more details see Alternative definitions of comma) For instance in Pythagorean tuning the diminished second is a descending interval (524288531441 or about −235 cents) and the Pythagorean comma is its opposite (531441524288 or about 235 cents) 5-limit tuning defines four kinds of comma three of which meet the definition of diminished second and hence are listed in the table below The fourth one called syntonic comma (8180) can neither be regarded as a diminished second nor as its opposite See Diminished seconds in 5-limit tuning for further details