Left: structure function variance (km⁴ s⁻⁴) averaged over 100 observations of a velocity field generated with the same underlying turbulent power spectrum (k_inj = 1/200 kpc⁻¹, k_dis = 1/20 kpc⁻¹) and corresponding ±1σ error bars as a function of the separation s (kpc). The comparison to the theoretical models derived from the simulation and the formulas by CL19 is shown for a circular FoV of R_in (blue solid), R_eq (red dashed) or R_ci (green dash-dotted). The sheer contribution of the cosmic variance without statistical terms for R = R_eq is given in light purple. Right: error contributions in the total variance for the previous case for R = R_eq when σ_stat, C = 34 km s⁻¹. The data points for the statistical and structure function fluctuation term are derived from analytical formulas, while the velocity field fluctuation term is computed using the 100 iterations (see text).