Black hole mass of 15 quasars, where the vertical and horizontal axes represent the black hole mass calculated with different methods. The red line corresponds to m_{bh − BL}(= M_{bh − BL}/M_⊙) = m_{bh − BL}(=M_bh − H/M_⊙), where M_{bh − BL}, M_bh − H, and M_⊙ are the black hole mass calculated with a broad line, the black hole mass calculated with the H band luminosity of the host bulge, and the solar mass, respectively. The average error is about 0.5 dex.