The wavenumber scales of the spectra can differ from one FT-IR instrument to the next. (They usually do.) This X-axis error is not usually very large. Frequently the X-shift is only one data point in the spectrum. This will not cause much trouble if one is working with the spectrum of a large molecule that has smooth bands. With a small molecule, however, a shift of one data point can cause disastrous results in spectral subtraction. See the topic SUBTRACTION ARTIFACTS. If there is an x-axis mis-match between the sample spectra and a quantitative reference spectrum, it may be necessary to correct either the sample spectra or the reference spectra. The sample spectra might be corrected by means of the parameters of the spectrometer operation, such as the designation of laser wavelength. The reference spectra might be correct by means of the X-shift program of the GRAMS software. Details are given in the GRAMS instruction manual.