Time evolution of the X-ray flux as measured by the GOES satellite in channel 1.0–8.0 Å (red) and 0.5–4.0 Å (blue). Upper panel: X-ray flux for the entire day 2015-05-05. Lower panel: C3.6 class flare in AR 12335. The blue area indicates the time of SST observation. The black vertical lines show the times of the three scans that we have used in our inversions, referred to as t_pre, t_peak and t_post.