The resolution and the frequency accuracy of a spectrum and the abundance of an absorbing gas can be obtained by ratioing observed and calculated spectra. Line positions (to ±0.002 cm−1), spectral resolution (0.075 ± 0.003 cm−1), and a CO abundance [(2.35 ± 0.23) × 10−2 atm-cm (STP)] have been found by comparing an observed CO spectrum with a spectrum calculated from the AFCRL line parameter listing.