Flux variation gradient diagram of 3C 120. The solid lines delineate the bisector regression model yielding the range of the AGN slope. The dashed lines indicate the range of host slopes determined by Sakata et al. (2010) for 11 nearby AGN. The intersection between the host galaxy and AGN slope (red area) gives the host galaxy flux in both bands. The two vertical dotted and dashed lines show the host flux determined by Bentz et al. (2006) and Bentz et al. (2009a) respectively. The solid line shows the host flux obtained by Sakata et al. (2010). The dash-dotted blue lines represent the range of the AGN flux in both filters. Fluxes (black dots) were measured in a 7.5′′ aperture photometry and corrected for galactic foreground extinction.