256/255

256/255, the septendecimal kleisma, diasemisma or 255th subharmonic, is a small 17-limit superparticular comma about 6.8 cents in size. It is the difference between 16/15 (classical diatonic semitone) and 17/16 (large septendecimal semitone, also called as minor diatonic semitone), and forms the amount by which a stack consisting of 15/8 and 17/16 falls short of an octave. It differs from 352/351 (the minthma) by 936/935 – an unnoticeable comma measuring about 1.85 cents.

Interval information

Ratio	256/255
Factorization	28 × 3-1 × 5-1 × 17-1
Monzo	[8 -1 -1 0 0 0 -1⟩
Size in cents	6.775876¢
Names	septendecimal kleisma, diasemisma, 255th subharmonic
Color name	17ug1, sugu 1sn, Sugu comma
FJS name	[math]\displaystyle{ \text{P1}_{5,17} }[/math]
Special properties	square superparticular, reduced, reduced subharmonic
Tenney norm (log2 nd)	15.9944
Weil norm (log2 max(n, d))	16
Wilson norm (sopfr(nd))	41
Comma size	small
S-expression	S16
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By tempering it out is defined the diasemismic temperament, which enables the diasemismic chords.

Etymology

The name diasemisma was named by Xenllium in 2023. It is a contraction of diatonic semitone into a single word; it is unrelated to the diasem scale structure. However, septendecimal kleisma and 255th subharmonic were attested much earlier.

See also

• Small comma
• List of superparticular intervals