A series of six interferograms was recorded to 4 cm^-1 resolution. The nominal data averaging time was 20 minutes, with 150 Hz 2 l_HeNe phase modulation on a TGS detector. Each resulting spectrum was ratioed to the next to produce this sequence of five 100% lines. The SNR is between 2000 and 3000:1 for all of the traces. They are tightly clustered around 100% T, but exhibit noticeable slopes.