Top panel: fractional disc coverage by plage as a function of time, derived with the NR thresholding scheme applied with the same parameters on images from the archives of Ar (red), Ko (blue), MM (pink), MD (brown), Mi (orange), MW (green), Sc/WS (dark green), and Rome/PSPT (black). Also shown are the plage areas from SFO (light blue). The numbers under the curves denote the conventional SC numbering. Bottom panel: sunspot areas from Balmaceda et al. (2009). Individual small dots represent daily values, while the thick lines indicate annual median values.