Examples of spectra. Top panel: small section of a high-resolution FTS spectrum of the Sun observed by Reiners et al. (2016). Middle panel: result of multiplying the raw spectrum with Eq. (1) (green line) with values of λ₀ corresponding to A and D in Fig. 1. Bottom panel: same, but with λ₀ corresponding to B and C. The FSR of the HMI E1 element and a contrast B = 100% were used. The Fel line around 6175 Å is the one used by HMI.