6561/6400

6561/6400, the double syntonic comma, is equal to two 81/80's stacked or (81/80)².

Interval information

Ratio	6561/6400
Factorization	2-8 × 38 × 5-2
Monzo	[-8 8 -2⟩
Size in cents	43.01258¢
Name	double syntonic comma
Color name	lagugu unison, Lgg1
FJS name	[math]\displaystyle{ \text{P1}_{5,5} }[/math]
Special properties	reduced
Tenney norm (log2 nd)	25.3236
Weil norm (log2 max(n, d))	25.3594
Wilson norm (sopfr(nd))	50
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Sagittal notation

In the Sagittal system, the downward version of this comma (possibly tempered) is represented by the sagittal  and is called the 25 small diesis, or 25S for short, because the simplest interval it notates is 25/1 = 5×5 (equiv. 25/16), as for example in E⁠ ⁠-B⁠ ⁠. The upward version is called 1/25S or 25S up and is represented by .