q profiles for centrifugally stable flows used in the calculation of β. The profiles are calculated using the spline fit presented in Fig. 6. Schartman (2008) used a finite difference method to evaluate q producing comparable results. q profiles are also plotted for ideal Couette fow, and marginal stability by the Rayleigh criterion q = 2. The stability boundary derived by Rayleigh (1916) and Taylor (1923) do not account for the presence of vertical boundaries. The oscillation in the QK(Split) case which occurs between 140 and 180 mm is due to the measurement of v_θ beginning before the flow had fully equilibrated.