Left: non-reduced Δχ² values obtained from NEMESIS retrievals of (D/H)_CH4 and temperature as a function of radiance offset. The three horizontal lines represent a Δχ² of 1, 4 and 9, which are equivalent to the σ₁, σ₂ and σ₃ levels, respectively. The dotted blue and dashed red lines mark the quadratic fits to the relevant regions. Right: change in the D/H ratio as a function of radiance offset. Derived values are marked by black crosses for each radiance offset. Quadratic fits to the radiance are marked for the same radiance offsets as in the left panel. For each of the confidence intervals, the radiance shift and its corresponding change in D/H is marked by σ₁ dotted (red and blue), σ₂ dashed (red and blue) and σ₃ dot-dashed (red only).