Investigated spectral region (topmost panel; blue trace: Hamburg, green trace: Liège) and the results from the fitting procedure (parameters L, S, B of Eq. (1), the rms of the residuals of the fit, and the reduced χ²) versus wavelength. The thin red tick marks and the bold blue tick marks above the topmost panel indicate grating order intersections and FTS scan intersections, respectively. Zero wavelength shift and unity scaling factors are indicated by the horizontal blue lines in the L and S panels. The blue line in the trace of the rms residuals indicates the median value.