Comparison of the stellar signal amplitude at short time scale for different stars (the Sun, HD 67458, and HD 88595). Left: comparison of the F8 metric computed on the 8-h subseries of VIRGO observations (red, green, and blue histograms) and CHEOPS observations of HD 67458 and HD 88595 (colored dashed and dotted vertical lines, respectively). The F8 metric has been slightly modified from the initial definition of Bastien et al. (2013) to include fluctuations evolving on timescales from 5 min to 8 h. F8 values computed on each TESS 8-h sub-series are shown for comparison (magenta and cyan histograms). Right: same for spectroscopic solar observations with GOLF (black histogram) and HARPS-N (red histogram) compared with ESPRESSO observations of HD 67458 and HD 88595 (colored dashed and dotted vertical lines, respectively).