Abstract: In a system for analyzing materials by near infrared analysis, a library of absorbance spectra from sample materials is stored in computer storage. The absorbance spectra of an unknown material is measured and is correlated with the library spectra to select those library spectra which most closely match the spectrum of the unknown material. The selected library spectra are used to determine, by least squares convergence, or by multiple regression, coefficients in equations relating measurable properties of the unknown material to absorbance measurements made on the unknown material.