The relation between the PDS break frequency and the orbital frequency of the binary system. The large shaded area toward the bottom of the plot is the widest region possible for the dependence f_visc vs. f_orb according to the α-disc, obtained from Eq. (1) in the mass ratio range 2.91 ≤ q ≤ 22.77 for α = 0.5. The dashed lines are predictions for larger values of the disc thickness H/R with α = 0.5 and q values indicated on the plot. Most of the errors in f_break are on the order of marker (or symbol) size.