Transmission spectrum of HAT-P-12 b obtained with HST WFC3 G141 using our CASCADe reduction. The top panel shows the spectra for the two observed transits (blue squares) and the combined spectrum binned to a uniform spectral resolution of 0.02 µm (black dots). The bottom panel shows a comparison of the spectrum derived in this study (blue dots) and the one derived by Tsiaras et al. (2018) (orange squares). In both panels, the band-averaged transit depth is indicated by the dashed horizontal line, and the shaded area represents its 95% confidence interval. The spectrum from Tsiaras et al. (2018) has been shifted downwards by 150 ppm to the same mean transit depth as found by CASCADe, for better comparison. The y-axis on the right is in units of planetary atmospheric scale height assuming a hydrogen-dominated atmosphere and an equilibrium temperature of ~500 K as derived from the ARCiS retrieval.