Average line-spread functions for the FGK stars (212 spectra) in the UVB (upper panel) and VIS (lower panel) arms. In each arm, the top panel shows the residual shift of the spectra (blue dots). The bottom panel shows the detected instrumental velocity dispersion. A simple first-order polynomial fit (red lines) of the line-spread function is marked in each panel. The error bars are the standard deviation in each wavelength bin. The three open circles show the region where two different flat field lamps are used in the UVB arm, which may result in larger uncertainties.