Fig. 4.
Top panel: overview of the structure and the coverage of the final composite of the corrected sunspot areas. Different colours (see legend at the top) show data from different observatories. Y-axis is the number of days per year, for which data are available. Bottom panel: pie-charts highlighting the percentage of contributions of observatories to the complete calibrated series (1874–2019: left chart) and only to the post-RGO period (1977–2019: right chart).
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