Each base pair sits at height y = i × 0.34 nm along the helix axis and at azimuthal angle θi = i × twist × (π/5.2) around it — the same rise-per-base-pair and per-base-pair twist used by the 3D model (twist = 1 gives ~34.6°/bp, close to real B-DNA's 34.3°). The two backbones are the same helix 180° apart; projecting the 3D (x, y, z) = (r cosθ, y, r sinθ) coordinates onto the canvas by dropping z (using only x for horizontal position, and z for depth-shading and size) reproduces the classic "rotating ladder" silhouette in pure 2D. Every rung is a real complementary base pair: adenine (blue) always opposite thymine (red), guanine (green) always opposite cytosine (yellow).