Semicomma
The semicomma, also Fokker's comma (after 31-TET pioneer Adriaan Fokker), is type of small musical interval, or comma, in microtonal music equivalent to 2109375:2097152, or . This is a ratio of approximately 1:1.0058283805847168, or about 10.06 cents (). It is derived from the difference in pitch between three 75:64 just augmented seconds () and one 8:5 just minor sixth () begun on the same root ((3 × 274.58) − (1 × 813.69) = 823.74 − 813.69 = 10.05 cents). It can also be viewed as the amount by which three tritaves exceed seven minor sixths. See also
Septimal kleisma
Septimal semicomma

References

5-limit tuning and intervals
Commas (music)