Representative example of relative flux, visibility, differential, and closure phase as a function of wavelength around the Brγ and Na I doublet emission towards IRAS 17163 using GRAVITY on the large configuration. The 6 baselines and 4 triplets of A0-G1-J2-K0 configuration are plotted with different colours. Both Brγ emission and Na I show a smaller visibility than the continuum while Brγ shows a larger drop. Mg II does not show changes in visibility or phases. A differential phase change is also detected towards Brγ but not towards Na I.