Negative-space torus

The torus is present only as an absence: the annulus between Ro and Ri is never painted, and nothing is drawn inside it. All marks sit on the two rims that bound it.

θ_k = 2πk/N + jitter · arc = 0.8 · completeness · 2π/N

Each mark k is an arc on the outer circle starting at θ_k, with a tiny deterministic jitter of up to 2° so the ring reads as drawn by hand rather than stamped. Ticking the inner rim repeats the set on Ri, staggered by half a step, so the two rims interlock.

The unpainted gap between them is what the eye completes — the boundary is carried by the ends of the arcs, which is why a small count (N between 6 and 12) and a modest completeness read as a ring, while a full circle would simply read as a circle.