J1807 spectra from the 2017 (left) and 2023 (right) outburst events. The colour code mark the X-ray state, similarly to Fig. C.2. The best fit corresponding with the parameters compiled in Fig. C.8 is shown as a solid blue line. Neither the DIB next to $\mathrm{H}\beta$, nor the nearby He I transition are present in the spectra, so they did not have to be masked out. The rest wavelength of the transition is marked with a black-dashed line, while blue-dotted lines mark velocity shifts of $\pm 2500\mathrm{km}{\mathrm{s}}^{-1}$ as a visual reference.