follows: spectra are adjusted in flux by a multiplicative constant that is determined by comparing each spectrum to a “reference spectrum” that has been formed by averaging all the highest-quality (i.e., typically signal-to-noise ratios $S/N \gtsim 30$) spectra and scaling this mean spectrum to the adopted ø5007 flux. All individual spectra are scaled relative to the reference spectrum in a least-squares fashion that minimizes the \[\] residuals in the difference spectrum produced by subtracting the reference spectrum from each individual spectrum. This program also corrects for small zero-point wavelength-calibration errors between the individual spectra, and takes resolution differences into account.

At this point, measurements of each of the spectra are made. The continuum flux at $\sim5100$Å (in the rest frame of NGC 4051, $z = 0.002418$, based on 21-cm emission \[deVaucouleurs et al. 1991\]) is determined by averaging the flux in the 5090–5120Å bandpass (in the observed frame). The  emission-line flux is measured by assuming a linear underlying continuum between $\sim4772$Å and $\sim5105$Å, and integrating the flux above this continuum between 4820Å and 4910Å (all wavelengths in the observed frame). The long-wavelength cutoff of this integration band is chosen to avoid the  contamination underneath \[\]$\lambda4959$. We also note that no 