That seems about right to me; most of the materials I use are graphs for certain kinds of exposures behind certain types and thicknesses of materials. That's really the kind of information we're interested in as engineers, but it doesn't mean much to someone who isn't contemplating building something. The numbers vary greatly depending on what conditions the compiler of the data has assumed. However, designing for longevity on the scale of years requires us to consider solar events, and so the average exposures according to many sources includes predicted numbers and strengths of these events.
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