Reverberation mapping is the principal method for determining the masses of the central black holes that power active galactic nuclei (AGNs). We discuss the importance of using line dispersion as opposed to full-width at half maximum (FWHM) as the line-width measure in computing AGN black hole masses to avoid biasing (stretching) the AGN black hole mass scale. We argue that narrow-line Seyfert 1 (NLS1) galaxies are, for the most part, the low-luminosity extremes of a class of objects that should be defined by accretion rate rather than simply by line width.