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Top curve. The ratio of annual RGO group counts to the yearly average of group counts of all observers (with RGO omitted; AllUNSC(−RGO)) from 1874 to 1920. Middle curve. The ratio of annual Wolfer group counts to the yearly average of group counts of all observers (with Wolfer omitted; AllUNSC(−Wolfer)) from 1876 to 1920. Note the offset of the left and right y-axis scales. Bottom curve. Annual sunspot number (SN*), 1874–1920. Dashed-line linear fits are given for the two top traces. The Vaquero et al. (2016) database (http://www.sidc.be/silso/groupnumberv3) was used for this analysis (with Mt. Wilson (Center of Disk) eliminated).
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