An example showing some of the worst baselines observed. The plotted spectrum is from an observation on April 2, 2014, showing the average of the 5% worst spectra. The blue curve shows a σ = 5 km s^-1 (FWHM = 11.75 km s^-1) line centered at the 0 km s^-1 position of p - H₂CO3_0,3−2_0,2, illustrating that the baseline “ripples” have widths comparable to the observed lines. While we selected the worst 5% in this case, nearly all spectra are affected by these sorts of baselines, and the shape and amplitude varies dramatically and unpredictably. The variation, unpredictable though it is, works in our favor as it averages out over multiple independent observations. The 218 GHz region shown here is also the worst-affected; the 220 GHz range that includes the ¹³CO lines generally exhibits smoother and lower-amplitude baseline spectra.