Plots illustrating velocity dispersion versus the number of stars, for different values of σ_μ, as calculated for the synthetic samples described in Sect. 4.1. Diagrams in the left column are for the projection method (PM), the right column is for the maximum likelihood method (ML). The symbols represent the different galactic components of the dispersion: σ_u (•), σ_v (▾), σ_w (▴). The true values are indicated by the horizontal lines.