Top panel: composite spectrum with prominent emission lines marked. Upper middle panel: measure of intra-spectrum variability. The standard deviation of the constituent spectra as a function of wavelength, where to normalize the differing slopes between the different spectra, the fitted slope in each of the constituent spectra have been subtracted. Lower middle panel: signal-to-noise ratio. The composite spectrum is divided by the error spectrum, thus directly giving a measure of the signal strength. Bottom panel: number of contributing spectra as a function of wavelength.