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2. Monthly-averages of the International Sunspot Numbers. Available on http://www.ssl.msfc.nasa.gov/ssl/pad/solar/greenwch/spot_num.txt
3. Predicted Sunspot Numbers are compiled by the United States National Oceanic and Atmospheric Administration (NOAA), Space Environment Center (SEC). Available on http://www.sec.noaa.gov/ftpdir/weekly/Predict.txt (accessed 9 March 2004).
4. Monthly-averaged Climax counting rate data obtained from the Solar and Upper Atmosphere Group, National Geophysical Data Centre, NOAA, Boulder, Colorado. Available on ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/COSMIC_RAYS/climax.tab.
5. International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60 (Oxford: Pergamon Press) (1991).