the unknown geometry and kinematics of the BLR, the virial mass is reliable to only about an order of magnitude, i.e., the systematic uncertainties are much larger than the errors quoted here. However, an independent estimate of the inclination of the system has been made by Christopoulou et al. (1997) on the basis of the NLR morphology and kinematics. These authors model the NLR as an outflowing biconical region of inclination 50 and half-opening angle 23. If the BLR and NLR axes are coaligned, then correcting the virial mass for inclination gives a central mass of $1.4^{+1.0}_{-0.6} \times 10^6\,\Msun$.

There are a number of important features in the rms spectrum that deserve attention: first, the constant components, such as the \[\]$\lambda\lambda4959$, 5007 narrow lines that are so prominent in the mean spectrum, are absent, as expected, in the rms spectrum (except for weak residuals which reflect the accuracy to which accurate flux calibration can be achieved). Second, the weak broad wings of  that can be seen in the mean spectrum are much weaker in the rms spectrum, i.e., the line core is more variable than the line wings. This could occur if the higher velocity material is much farther away 