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In-orbit experience has shown that the background in the short-wavelength filter (``S1'') is dominated by cosmic rays and by a spacecraft related spacecraft glow phenomenon. In the shorter wavelength filters additional components are present due to resonantly scattered photons from the strong emission lines in the solar spectrum (most notably the line of He II). Table 6.4 gives the approximate ranges and orbit-averaged count rates for each of the background components, Tab. 6.5 gives the typical overall background rate in each filter. It should be stressed however that all of the components (with the exception of the MCP intrinsic noise) are time variable with periods ranging from minutes to months, dependant on the component concerned.