Top: TSI reconstruction with the SATIRE-Ca model using Meudon Ca II K data (black dots for daily and orange line for 180-day running means) along with the Montillet et al. (2022)TSI composite (green line). The running means are computed only over the common days in the two series. Bottom: Difference between the TSI reconstructed with SATIRE-Ca using Meudon Ca II K data and the PMOD TSI composite. Daily values are shown as black dots and 180-day running means as orange lines. The right panel shows the histogram of the residuals in bins of 0.04 Wm⁻². Vertical dashed lines mark periods of discontinuities in the Meudon Ca II K data. In particular, the black line marks the improvement of the system over 2017 along with reduction in bandwidth of observations, the purple lines mark the period when the switch between photographic plates and CCD camera occurred in 2002 (there was an overlap of CCD and photographic data, thus the lines mark the first application of the CCD camera and the last day that photographic plates were used), while the photographic data outside of the two red lines were derived from a different digitisation than the other data. The dashed horizontal ciel line marks the level of Montillet et al. (2022) TSI composite during the 1996 minimum in the top panel and residuals of 0 Wm⁻² in the lower panel. The numbers in the lower part of the figure denote the conventional cycle numbering.