Residuals from different interpolation schemes over pixels in echelle order 100. ThAr lines, shown as blue circles, are used to construct a wavelength solution that is then evaluated at each LFC line, shown as blue vertical lines. The residuals of each wavelength solution for a subset of the order are shown on the left. Histograms of the residuals for each method for the complete order are shown on the right. Note: There is a blended ThAr line at approximately pixel 5300, the rightmost ThAr line plotted.