Tertium minor

In harmony, the tertium minor is the ratio 6:5 between a pair of frequencies or, equivalently, the ratio 5:6 between a pair of wavelengths. It is the harmonic mean of unison and diapente:

It is equal to diapente divided by tertium major:

This means that diapente is equal to a tertium major and a tertium minor, put together.

Tertium minor 1.00110011001100110011... in binary, and it is the inversion of the major sixth (5:3), viz.

The major sixth is the sum of the first five reciprocals of triangular numbers:

Tertium minor is also called the minor third.

See also: tertium major.