Top-left panel: centripetal acceleration curves in g2 space of MOND MI (solid grey curve) and MOND MG in the Brada-Milgrom approximation (black dotted curve) with acceleration scale g₀ = 1.2 × 10⁻¹⁰ m s⁻² for a 3MN model of an infinitely thin exponential disc galaxy with M = 1.2 × 10¹⁰ M_⊙ and a scale length of r_d = 3.5 kpc. The 3MN parameters are given in the appendix. The dotted coloured curves are the full MOND MG solution of the same model but with the scale height parameter of the 3MN model varied: b = 3 (green), b = 1 (red), and b = 0.3 (blue) (b → 0 is the disc limit, and b → ∞ is the spherical limit). Finally, the solid orange line gives the purely Newtonian acceleration. Top-right panel: corresponding rotation curves showing the full MOND MG solution only for b = 0.3. Bottom-left panel: corresponding curl field S for the b = 3 case, showing how the curl field at z = 0 is in the opposite direction to the Newtonian one and how it reduces the radial MOND MG acceleration compared to the MOND MI. Bottom-right panel: difference in curl fields for the most disc-like (b = 0.3) and most spherical (b = 3) parameter values, showing that the solenoidal field reduces the radial MOND MG acceleration in the z = 0 plane most for the most disc-like mass distributions.