* Once you have the correct grating in the spectrograph, enter an approximate starting angle (see the grating table above) in the ''Grating angle'' box and click ''Go''.
* Take an arc and check the wavelength range on the Quick-Look extraction that will appear shortly after the image is read out. Note that it is advisable to double check the arc by displaying the spectrum in e.g. pyRAF, as the Quick-Look plot doesn't always display the arc lines at the end of the wavelength range.
* If the spectrum is too blue (red), decrease (increase) the grating angle and repeat the arc to check the new wavelength range - iterate until happy with the range.