Standard deviation as a function of bin size for a bin centered on the Na I core in various cases. Shown are the prediction from photon noise (purple dotted–dashed), the standard deviation measured in the real data (black solid line), and the standard deviations predicted by the simulation due to only the shift (blue dotted) and in the case where the shift has been corrected (green dashed). All standard deviations are normalized to the out-of-transit flux. Shown with a dashed red line is the bin size used for the majority of the transmission spectrum, which is 30 pixels or 10 nm.