Comparison of HST/WFC3 transmission spectra for three different data reduction and fitting methods for HD 209458 b. The blue spectrum uses exponential functions to fit the systematics at the beginning of each orbit (model_ramp fit), whereas the green spectrum assumes wavelength independent systematics (divide_white fit). The grey spectrum is the original transmission spectrum published by Deming et al. (2013). The right panels show the differences between all three spectra. Noticeable is the linear trend with wavelength in the residuals for all three cases.