Nothing here is drawn by hand. Every centre sits on a grid intersection, every straight edge on a grid line, and every curve is a circular arc — SVG A commands only, no bezier control points.
The swash works because 13 and 11 are both odd. Centres equidistant from both corners of a 13 × 11 box lie on the perpendicular bisector of its diagonal, C(t) = (6.5, 5.5) + t·(−11, 13), and every half-integer t on that line lands on an exact grid point: (1,12), (12,−1), (−10,25), (23,−14). Their radii come out √145·u and √725·u — a ratio of exactly √5.
A rectangle eight units wide closed by a circle of radius 5u centred on the intersection (8, 5). Because the radius is exactly half the height, that circle is tangent to the top and bottom grid lines — the arc joins the straights with no flat spot and no corner. All four remaining corners are grid points.
Two arcs strung between the same two grid points — the opposite corners (0, 0) and (13, 11). Each is a plain circle centred on a grid intersection. Pick a near centre for a tight dive, a far one for a flat sweep; because both circles pass through both corners by construction, the tips stay pinned however you pair them. Matching the reference takes the far centre outside and the near centre inside.