Comparison of spectral features in the COS (black) and STIS (red) spectra of Mrk 509. Normalized relative fluxes are plotted as a function of velocity relative to the systemic redshift of z = 0.034397. The boundaries of the 9 absorption troughs used in our analysis are shown along the top (see Table 1). The centroids of the individual Gaussian components identified in Paper VI are shown by the vertical dotted blue lines.