If the spectrum is labelled as an '''arc''' in the header, the QL tool will attempt to perform automated wavelength calibration. This is generally robust and no changes of settings should be needed. For the less frequently used gratings or for unusual grating angles, the default parameters may not work so well, and so notes for advanced users to change settings to the fitting routine are provided here https://topswiki.saao.ac.za/index.php/Quick_Look_Tool#WLC_advanced_tab .
After wavelength calibration of an arc, a '''library reference spectrum''' will be overplotted in green allowing the user to quickly check the quality of the calibration. As mentioned in the introduction, this is intended to be a quick look calibration at the ~2A level and solutions should must be refined by the user if greater precision is needed to meet the science requirements. As a further aid, the wavelength of the midpoint of the spectrum is printed to the bottom of the screen, allowing the observer to monitor any possible drifts in the wavelength coverage.
Should the user, for some reason, not want to use the wavelength calibration, or just view the data in pixel units, the '''"ignore WLC"''' button may be used. In this case, the output extracted spectrum written will also only contain the pixel solution. To retrieve the wavelength solution, reload the arc by pressing "Update" next to the Current Frame box.