Backtracked half-mass radii for a simulation with 4000 stars, Top: calculated using actual masses (green), 0.2 M_⊙ (red), 0.3 M_⊙ (blue) and 0.5 M_⊙ (yellow). Bottom: calculated using exact velocity values (green), using v_z = 0 (red), using velocities values with systematic errors as well as different levels of statistical uncertainty (blue: 0.27 km s⁻¹ and yellow: 1 km s⁻¹). The actual values of t_emb and r_hm at the time of gas expulsion from the simulation are shown in cyan.