Delta gain derivation results for bands 1–3. Dots correspond to individual gain measurements; lighter-coloured dots have a lower level of confidence, and therefore a lesser weight in the fit. Black dots originate from in-orbit observations (Sect. 3.2), while mint crosses originate from laboratory methanol data (Sect. 3.1). The red line shows a smoothing cubic spline through the points. The green dashed line shows the prior gain. The black line represents a balanced mixer, i.e. delta gain = 0.