A stochastic model for the energy source of QSO's is used to fit the light curves of 43 objects taken from long-period photometry (minimum duration of observations, 8 years per object). The model fits are encouraging enough to allow us to derive absolute luminosities for individual QSO's and to re-plot the Hubble Diagram with the values thus computed. We find a significantly improved fit to the expected unit slope in the plot of log z against 1/5(mB - MB), and a best fit value of qo = 0.1 (±0.4).