40/39

Interval information

Ratio	40/39
Factorization	23 × 3-1 × 5 × 13-1
Monzo	[3 -1 1 0 0 -1⟩
Size in cents	43.83105¢
Names	tridecimal 1/5-tone, tridecimal minor diesis
Color name	3uy1, thuyo unison
FJS name	[math]\displaystyle{ \text{A1}^{5}_{13} }[/math]
Special properties	superparticular, reduced
Tenney height (log2 nd)	10.6073
Weil height (log2 max(n, d))	10.6439
Wilson height (sopfr(nd))	27
Open this interval in xen-calc

40/39 is the difference between the third octave of the third 5/4 (40 = 5 ⋅ 2³) and the fifth of the thirteenth partial of the same root (39 = 13 ⋅ 3). If tempered out, it equates 39/32 with 5/4 and thus 6/5 with 16/13, so that it does not assosciate major with greater neutral and minor with lesser neutral as one would expect (see 65/64), but the other way around.

Sagittal notation

In the Sagittal system, the downward version of this comma (possibly tempered) is represented (in a secondary role) by the sagittal ⁠ ⁠ and is called the 13/5 small diesis, or 13/5S for short, because the simplest interval it notates is 13/5 (equiv. 13/10), as for example in C-F⁠ ⁠⁠ ⁠. The primary role of ⁠ ⁠ is 6400/6561 (25S). The upward version is called 5/13S or 13/5S up and is represented (in a secondary role) by ⁠ ⁠.