Results of the Jeans modelling of M3. Models were calculated over a grid of constant mass-to-light ratios Υ and black-hole masses M_BH. Left: distribution of likelihoods in the M_BH − Υ plane. Contours trace the 1, 2 and 3σ confidence intervals. Centre: one-dimensional likelihoods as a function of M_BH (solid line) and Υ (dashed line), respectively, obtained by marginalizing the two-dimensional distribution over the other parameter. Horizontal dotted lines indicate the 1 and 3σ confidence limits. Right: comparison between the data and the velocity dispersion profiles predicted by the models with the most likely mass-to-light ratio and a range of black-hole masses, as indicated in the plot.