Two upper panels: spectra for HD 130163 with the most discrepant calibration of the UV flux slope. The steps to determine D_⋆ are indicated in red: selection of continuum points to fit the slopes and the difference between the two fits at 3700 Å as the value of D_⋆. In blue for λ₁: the midpoints between the continuum fits in red, the upper envelope of the BD. The intersection of this envelope with the midpoints to determine λ₁. Lower panel: for HIP 25007, a clear double BD is present, and the Balmer continuum must be determined by choosing bona fide continuum points manually.