Linear correlation between log N, log  Q^1/2 and log  v_slip. a) log N as a function of log (v_slip /) for Line A (yellow) and Line B (purple) with v_slip obtained from third-order spline interpolation. b) log  Q^1/2 in function of log (v_slip / with the same color-code and for the same interpolation scheme. c), d) Same graphs, but with v_slip measured with a linear interpolation method. The function f(v_slip) = log   (v_slip) − log   (v_QSL) is added to all the graphs, with v_QSL = 0.0373 for line A (black) and v_QSL = 0.0318 for line B (red), see Fig. 9.