Testing convergence with respect to the size of our large-scale grid. We show the 21 cm power spectrum of CDM as a function of k at z = 20, 30, and 40, for three box sizes: 1536, 768, and 384 Mpc on a side, corresponding to 512³, 256³, and 128³ pixels, respectively. The curves go down to k = 0.01, 0.02, and 0.04 Mpc⁻¹, respectively. We note that the precise output redshifts that we use from the numerical simulations are 19.46, 30.00, and 39.89 (which we loosely refer to as 20, 30, and 40).