Hβ and best-fit model light curves of 3C 120. The interpolated Hβ light curve is shown with red crosses. Note the sharp drop of the light curve at days ~110 and ~130 as well as the sharp feature at days ~150 and the strong rise at day ~170. Both the spherical BLR model (black dotted line) and the inclined thin disks (i = 45° blue solid line, i = 60° green solid line) fail in fitting these sharp variation features. The features are best fitted by a thin-disk BLR model with inclination i = 10° (black solid line). Already at i = 20° (violet solid line) the thin disk fit yields a poorer chi-square. The light curves are shown only after the initial settling-down phase (~60 days), to account for the unknown continuum light curve before day zero.