  We published spectra of phosphine molecules in Venus' clouds, following
open-science principles in releasing data and scripts (with community input
leading to ALMA re-processing, now benefiting multiple projects). Some
misconceptions about de-trending of spectral baselines have also emerged, which
we address here. Using the JCMT PH3-discovery data, we show that
mathematically-correct polynomial fitting of periodic ripples does not lead to
"fake lines" (probability < ~1%). We then show that the ripples can be
characterised in a non-subjective manner via Fourier transforms. A 20 ppb PH3
feature is ~5{\sigma} compared to the JCMT baseline-uncertainty, and is
distinctive as a narrow perturber of the periodic ripple pattern. The structure
of the FT-derived baseline also shows that polynomial fitting, if unguided, can
amplify artefacts and so artificially reduce significance of real lines.
