Each disc magnet is treated as a uniformly magnetized cylinder, equivalent at a distance to a magnetic dipole of moment m = M·V = (B_r/μ0)·V. For two identical coaxial dipoles separated centre-to-centre by r and aligned along the shared axis, the on-axis force between them is
F = 3·μ0·m1·m2 / (2π·r⁴)
and the axial field of a single dipole at distance z is B(z) = μ0·m / (2π·z³). In the "attract" orientation the two gap-side fields reinforce at the midpoint (Bmid = 2·B(r/2)); in the "repel" orientation they cancel exactly on the symmetry plane, which is why the field readout drops to zero there even though the poles are pushing hard apart.
Temperature affects NdFeB in two distinct ways modeled here: a reversible remanence loss of about −0.12 %/°C (recovers fully on cooling), and, once the magnet crosses its grade's maximum operating temperature, an irreversible knee-point loss that keeps reducing Br permanently — cooling back down does not undo it; only a strong remagnetizing pulse (the "Re-magnetize" button) restores full flux.
- Field lines — traced from a two-pole (north/south) magnetic-charge model of each disc, the standard way to draw a real bar-magnet's external field.
- Grades — N35/N42/N52 differ in remanence and in how much headroom they have before the irreversible knee (higher-energy grades tend to have lower rated max temperature).