Probability density function for occurrence of the annual group sunspot numbers for the years 1848–1918. Panel A) the red solid line represents the years (50 years) without naked-eye spot (no-NES) reports, while the blue dotted line represents only the years (21 years) with NES. Panel B) the difference between the no-NES and NES probability density functions. Error bars represent the 1σ statistical uncertainties.
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