The EUV spectrum of the Sun: long-term variations in the SOHO CDS NIS spectral responsivities G. Del Zanna, V. Andretta, P. C. Chamberlin, T. N. Woods and W. T. Thompson A&A, 518 (2010) A49 Published online: 02 September 2010 DOI: 10.1051/0004-6361/200912904