  Motivated by STIS observations of more than 50 nearby galactic nuclei, we
consider long-slit emission-line spectra when the slit is wider than the
instrumental PSF. The finite width of the slit generates complex patterns in
the spectra that can have considerable diagnostic power if they are modeled
with adequate sophistication. They allowed us to develop a new method for
estimating the BH mass that gives fuller information and higher sensitivity to
BH detection than traditional methods.
