This figure shows the time dependence of the SWP NEWSIPS and IUESIPS extractions (MXHI and MEHI files, respectively) for large aperture spectra of eta UMa. It shows a ratio of the mean of 10 high dispersion spectra obtained in 1993-94 divided by 10 spectra obtained in 1981-82. The solid curve is the ratio of NEWSIPS extractions, and the dashed curve is a ratio of IUESIPS extractions. Both sets of data were binned to 0.5 Å/point.
The distinctive ripple pattern in the NEWSIPS spectra implies that spectra obtained 12 years apart will contain systematic differences on the order of 10% throughout most of the wavelength range, and up to 30-40% shortward of Ly alpha. The IUESIPS data do not suffer from this problem, but they do show the wavelength dependent signature of camera degradation (which was not corrected for in IUESIPS high dispersion data).