Comparison between the PDF of the orbital velocity (6026 pairs with accurate radial velocities, blue curve with its error bars) and the PDF of (GM/r_p)^1/2, where the pair masses M are obtained from their luminosity L through a constant M/L ratio, M = μL (red curve). An excellent agreement between the two curves (everywhere within ±1 sigma) is obtained by fitting the M/L ratio to the value μ = 33 ± 7. The uncertainty was estimated by varying the value of μ (orange curves, μ = 26 and 40).