Distribution of Β_x in the simulations of the Kelvin–Helmholtz instability at t/t_max = 1/6 for different grid resolutions, starting from the initial conditions described in Sect. 5.3 with ℳ_x = 10⁻³. On grids with N ≤ 128, numerical discretization errors generate grid-scale vorticity, which leads to the growth of secondary instabilities in the regions between the primary rolls. This effect does not appear in better converged simulations.