Mean (left) and variance (right) of M(S_X(N_gal))/M(S_true) as a function of N_gal for the case of Gaussian random velocities. The dashed line in the left panel represents the expected analytic formula for the dependence of F(S_std) on N_gal for the standard deviation described in Appendix A. Green, red, and blue lines represent the behaviour of the standard deviation, gapper, and biweight estimators, respectively.