Asymmetric case for a disk-like BLR such as 3C 120 (i = 10°, R_min = 22 light days, R_max = 28 light days, v_max = 2850 km s^-1). Top: NB filter ([OIII]λ 5007 Å, dotted line) and emission-line profile of the BLR (Hβ, thick solid line). The filter essentially covers the complete blue half of the Hβ line, as is the case for 3C 120. Bottom: BLR areas inside (black) and outside (coloured) of the NB filter. The colour-coding (blue, green, red) indicates a line transmission of about 50%, 20%, and 0%.