The UES A&G unit provides a range of comparison lamps (both emission line
and continuum), and neutral density, polarizing and colour filters. The UES
Manual gives a full listing. The present set of neutral density filters is known
to introduce a ripple in the signal at a level of a few percent peak-to-peak;
possible replacements are currently being considered. Wavelength calibration
normally uses a Th-Ar hollow-cathode reference lamp.