χ² behavior of the spin a for the broken power law emissivity disk profile (Model 3). All four observations have their best minima at a ~ 0.9. Obs1 is drawn with solid, Obs2 with dashed, Obs3 with dotted and Obs4 dot-dash-dotted line. The zoom-in figure shows the area around the minima, produced with very fine binning. Similar behavior is produced for the single power-law profile.