Correlation between daily values of the solar S-index from TIGRE (in the Mount Wilson scale) and the USET area fraction. Top panel: plages only, A_P. Bottom panel: plages and enhanced network, A_PEN. The parameter n represents the number of data, and the chronological order is color-coded. The first and last date of the data are given next to the color bar. Additionally, a linear fit was performed to the data (red solid line). A mean error bar is displayed on the bottom right corner to have an idea of the uncertainties on the data.