FIELD: methods of initial calibration or recalibration of the second spectrometer in light of the first spectrometer, or, respectively, of itself. SUBSTANCE: during calibration use is made of selection and processing of spectral data obtained both from the first and also from the second instruments. In calibration, use is made of selection and processing of spectral data from the same first instrument which are obtained both, before and after necessity in recalibration arises. Instead of modification of corresponding characteristics of the first and second instruments or the first instrument, before and after arising of necessity in calibration, the present invention modifies the equation of calibration of the second instrument or recalibrated instrument for obtaining results compatible with the results obtained from the first instrument or by the first instrument before it comes out of calibrated state. Equation of calibration is such equation which converts the spectral data of concrete specimen in multitude of wave lengths in compliance with calculated value for some chemical or physical property. Usually the form of such equations of calibration is linear combination of spectral absorbing ability or mathematic conversion of values of absorbing ability measured by the first and second instruments for each specimen. EFFECT: preserved or in some cases even improved accuracy of primary calibration or recalibration of instrument. 10 cl, 8 tbl
