Tonic, voice, and display.
How the wheels and stars are drawn.
A real Spirograph gear can only draw figures whose lobes divide the circle evenly — 2, 3, 4, 6, or 12 on a 12-note clock. These eleven wheels draw every count from 2 to 12: the divisor wheels are honest round gears, and the impossible counts — 5, 7, 8, 9, 10, 11 — get the warp.
The trick is the same one behind the oval cogs in old gear sets: the drawing plane is gently stretched, sector by sector, so every lobe lands exactly on a note. Each wheel carries the most evenly spread set of its size — 5 draws {0,3,5,7,9}, 7 draws {0,2,4,5,7,8,10}, 8 the octatonic {0,1,3,4,6,7,9,10}, and 9, 10, 11 fill in all but the most symmetric leftovers.
Wide lobes cross big intervals; narrow lobes mark the half steps — the figure is a picture of the set's interval structure, drawn in mirror symmetry about the vertical 0–6 axis. Watch the gear itself squash and stretch as it rolls: that is the warp at work.
Crank forward to sing the notes ascending; crank backward to descend. Every figure closes where it began, ending on the home note one octave higher. Round, Point, and Loop move the pen on the wheel — same music, a new outline.
Tap Fill to fill every lobe with its note's Harken color, topped with a center disc — white, black, or tonic-colored (Settings). Layered figures stack as concentric rings. Tap again for line art; nothing is ever lost.
The five ✦ stars at the end of the shelf are a different animal. Instead of stepping around the clock in order, they connect the notes in fifths — every line a leap of seven — so the chords cross the middle and the points touch the ring. Crank forward for rising fifths, backward for fourths; the biggest star strings all twelve notes into one unbroken path that closes right where it started. It is the same circle of fifths that draws the Harken galaxy. Round, Point, and Loop bend the star's lines, and Fill paints it like stained glass.