Amplitude bias of the 3-dimensional estimator for the masked NVSS geometry of Singal (2011). Data represent mean and empirical variance of 1000 simulations for each N. A function is fitted to the simulated data, with best-fit values A = 0.883 ± 0.006, KD = (0.642 ± 0.005) × 10^-2 and A = 0.847 ± 0.016, KD = (1.59 ± 0.008) × 10^-2 for the expected kinetic radio dipole and the radio dipole measured by Blake & Wall (2002), respectively. The simulated dipole amplitudes, without masking, are indicated by the horizontal lines.