Convergence as a function of the radial resolution, taken as the relative frequency differences between computations using consecutive radial resolutions, r and (r + 1) points, at three different rotational velocities: 18.5%   Ω_k in green, 37.9%   Ω_k in light blue, and 58.9%   Ω_k in dark blue. In both panels, the mode is dominated by the ℓ = 2, m = 0 component. The upper panel corresponds to an n = 3 mode and uses irregular grids, whereas the lower panel shows an n = 9 mode calculated with even distributions of points.