Wavelength calibration is necessary so that spectral features can be identified. ORAC-DRcurrently only calculates a wavelength estimation based on information contained in the FITS headers. It takes the values for dispersion and central wavelength, then applies these values as a linear wavelength scale to the spectral image.
This is often not good enough for accurate wavelength calibration
as most grisms and dispersers produce higher-order dispersions, so
manual wavelength calibration must be performed after spectra have
been extracted.
[_WAVELENGTH_CALIBRATE_BY_ESTIMATION_]
ORAC-DR -- spectroscopy data reduction