Comparison of M_BH of Al III and C III], along with their residuals. Upper panels: log space of M_BH(Al IIIλ1860) vs. M_BH(C III]λ1909) computed with the scale relations of M22 and VP06 for the Pop. * sources [FWHM(C III]) ≠ FWHM(Al III)]: a) log M_BH(Al III) vs. log M_BH(C III]) both using M22 SR; b) log M_BH(Al III) using Eq. (3) by M22 vs. Eq. (7) by VP06; c) log M_BH(C III]) using Eq. (4) by M22 vs. Eq. (7) by VP06. Lower panels: residuals of each M_BH computation, δlog M_BH. Colour-code are the same as for Fig. 9. The dashed line traces the 1:1 relation, the solid line is the best fit obtained using the least-square method, and the red line is the median value of δlog M_BH. The uncertainties of the Pop. * sample are marked with a cross and calculated as the sIQR.