Top panels: daily TSI from the PMOD composite (black) and reconstructed (red) from Ca II K observations from the BB (left) and Ka datasets (right). Also shown are 81-day running mean values (dashed ciel lines for the reconstructions and black solid lines for the PMOD composite) but only for the days, when both PMOD and the respective reconstruction are available. Bottom panels: difference between the PMOD TSI series and the reconstructed TSI. The ciel line shows the 81-day running mean, while the dashed blue line is a linear fit to the residuals. The horizontal dotted black lines denote zero difference. The numbers at the bottom of the panels indicate the solar cycle number and are plotted at roughly the maximum of each cycle. Periods with known instrumental or observational changes are marked with vertical dashed purple lines (see Sect. 5.2 for more details).