Steps of the re-normalisation of spectra for TIGRE S_{II_MWO} estimation: upper panel shows the Ca II H&K region of HD 29139 taken with TIGRE on December 27 2019; the middle panel shows the continuum-normalised spectra of the TIGRE spectrum as a black line and the selected and continuum-normalised PHOENIX spectrum as a red line, and the lower panel shows the re-normalised TIGRE spectrum as a black line and the PHOENIX spectrum in a relative flux scale (flux divided by the maximal flux).