The note wheel figure

The wheel is the app's picture of a set of notes — a scale, a chord, a pentatonic — with the instrument taken away. It appears all over the site, mostly small: on the chips above an instrument figure, beside a concept's title, in the theory tour, inside the circle of fifths and as the whole of the harmonic field.

What it shows

Twelve wedges round a clock, one for each semitone, the root at twelve o'clock and the semitones running clockwise. A note in the set is an open wedge; a note outside it is closed — collapsed onto its own center line, so it isn't seen and the disc shows through. The wheel says one thing: which of the twelve are in, at what distances from the root.

The colors are the degree colors — the same twelve as the glyphs on the instrument — and they go by distance from the root: the root's wedge is always the root color, the fifth's always the fifth's. A major triad is three wedges at 12, 4 and 7 o'clock; a major scale is seven, with the two gaps where its semitones are; the chromatic scale is the full disc.

Because the root is always on top, two wheels are compared by shape alone. A major and a minor triad differ by one wedge moved one step. The seven major modes are one shape turned — the same seven wedges with a different one at the top — and that is the whole idea of a mode, drawn.

How it moves

When a wheel changes set it doesn't repaint: wedges that leave close first, then the wedges that arrive open — so you see what went and what came. One note moving to the next semitone (a major triad becoming minor, a maj7 becoming a 7) is a wipe: the old wedge retreats into the edge it shares with the new one while the new one grows out of it.

A run of modes is a turn: the notes stay lit, the wheel spins so the next home sits at the top, then every wedge closes, the colors shift so that home wears the root color, and every wedge reopens. The chords inside a scale are drawn out of it one at a time: each chord's notes marked on the scale in turn — root, third, fifth — then the rest of the scale closes and the chord stands alone, recolored from its own root, then the scale comes back and the next degree is up. The four wheels above are these four things, on the app's own period.

A marked wedge stands out a little from the rest — the app's way of pointing at a subset while the whole set stays lit.

Where it appears

• On the chips above an instrument figure: the chip is the set's wheel, so a page never draws a second row of them.
• Beside a concept's title on its page, when the concept is one set, with its facts on a line under the name.
• In the theory tour and the explorer on the NoSheet page, where every stop's wheel moves through its sets on one shared period.
• In the play panel on the home page, on the stops that have sets to show.
• As the inner ring of the circle of fifths figure, the same notes in pitch order.
• As the big wheel and the row of small ones in the harmonic field figure.

Wherever it stands, the rule is the same: home on top. The site never draws a wheel with C fixed at the top the way a textbook circle does; a change of key is a spin, and the shape of the set is what you read.