Residuals of a single LFC exposure plotted with respect to detector position (as defined by echelle order and x-pixel) for parametric (left) and nonparametric (right) wavelength calibration methods. Each line is colored by the difference between the predicted wavelength and the theoretical wavelength for each line, given in units of meters per second. High-order structure, i.e., vertical stripes and patchiness, is apparent in the residuals to a polynomial wavelength solution, which assumes smoothness.