21-tet scale on C (57.14 cent steps). Easley Blackwood, Jr.'s notation for 21 equal temperament. Intervals are notated similarly to those they approximate and there are distinct enharmonic equivalents (E-sharp-down = F-down). MIDI pitch bend matches intervals.
<a href="//commons.wikimedia.org/wiki/User:Hyacinth" title="User:Hyacinth">Hyacinth</a>
<span class="int-own-work" lang="en">Own work</span>