A modified Beckman IR-7 prism/grating infrared spectrophotometer has been calibrated with an absolute accuracy of up to ±0.05 cm-1 from 630 cm-1 to 2050 em-1, and with an absolute accuracy of the order of ±0.10 cm-1 from 2000 cm-1 to 4000 cm-1. This represents an improvement over the manufacturer’s specifications by factors ranging between 10 for the longer wavelengths and 50 for the shorter wavelengths. The frequency reproducibility of the modified instrument and the linearity of the frequency (wave number) presentation have been critically examined.
Peter J. Krueger, "Performance of the Beckman IR-7 Infrared Spectrophotometer I. Frequency Reproducibility and Accuracy (630-4000 cm-1)," Appl. Opt. 1, 443-453 (1962)