The note wheel figure
Twelve wedges round a clock, one a semitone, the root at twelve: a set's notes are open, colored by their distance from the root, the rest closed — and a change of set opens and closes them.
The wheel is a set of notes with the instrument taken away: twelve wedges round a clock, one a semitone, the root at twelve. A note in the set is open, a note outside it closed. Tap a wheel and the text follows it.
A set changing
Wedges that leave close first, then the wedges that arrive open — so you see what went and what came. Chromatic to major to pentatonic to triad, and back. The colors are the degree colors, the same as on the instrument: the fifth's wedge is always the fifth's color.
One note moving
When one note moves a semitone — a major triad turning minor — the old wedge slides into the edge it shares with the new one, and the new one grows out of it.
The modes
The notes stay lit and the wheel turns so the next home sits at the top; then every wedge closes, the colors shift so the new home wears the root color, and the wedges reopen. Seven major modes are one shape turned seven ways — that is the whole idea of a mode, drawn.
The chords inside
Each chord of a scale is drawn out of it in turn: root, third and fifth marked one after another, then the rest of the scale closes and the chord stands alone in its own colors, then the scale comes back and the next degree is up.
Where you'll meet it
Everywhere, mostly small: as the chips above an instrument figure, beside a concept's title, in the theory tour on the NoSheet page, as the inner ring of the circle of fifths and as the whole of the harmonic field. Home is always on top, so two wheels are compared by shape alone.