Effect of the finite box size on the precision of our numerical simulations. Three-dimensional velocity dispersion ΔV_3D in each of the 100 numerical realisations for the three configurations in Table 1 is shown as blue histograms. Vertical dashed line indicates the exact value of σ_turb from integration of the input turbulent power-spectrum (Eq. (14)). The increased numerical dispersions in those values as L_inj increases as a consequence of the finite simulation box size.