Transmission spectrum of WASP-103b zoomed in on the Na (top) and K (bottom) features. The black points refer to the 10 nm wavelength bins also shown in Fig. 6, blue points indicate 2 nm bins centered on the features: either one bin centered on the Na feature, or two point centered on each component of the K feature. In the lower panel, brown refers to a 2 nm wide bin centered between the two components. Red and orange points denote wavelength bins of 5 and 10 nm width, respectively, centered on the features. The solar-composition model spectrum is shown in green, and filled circles indicate the model binned to the resolution of the data.