A method for providing a regression model for calibrating a plurality of structurally identical spectrometers for ingredient analysis; comprising the following steps: - providing a multiplicity of samples which contain an ingredient in different concentrations; - measuring the concentrations of the ingredient in the individual samples using a reference measurement method to obtain reference measurement values for the concentrations of the ingredient; - measuring spectra of the individual samples with a spectrometer selected by way of example from the structurally identical spectrometers; - determining a preliminary regression model in which amplitude values of the measured spectra form the independent variables and in which the reference measurement values of the concentrations of the ingredient form the dependent variable; - selecting at least one spectrum from the measured spectra and/or an average spectrum formed from the measured spectra according to a suitability for predicting the concentration of the ingredient; - simulating tolerances of components of structurally identical spectrometers multiple times with a mathematical model of structurally identical spectrometers to obtain a multiplicity of error spectra; - adding the individual error spectra respectively to the selected spectrum or to the individual selected spectra to obtain simulated spectra; - applying the preliminary regression model to the simulated spectra to obtain in each case a prediction value for the concentration of the ingredient; - selecting a number of the simulated spectra, wherein the prediction values obtained for the selected simulated spectra depict a variation of the prediction values obtained for the simulated spectra; and - determining a resulting regression model in which amplitude values of the measured spectra and the selected simulated spectra form the independent variables and in which the reference measurement values of the concentrations of the ingredient form the dependent variable. - providing a multiplicity of samples which contain an ingredient in different concentrations; - measuring the concentrations of the ingredient in the individual samples using a reference measurement method to obtain reference measurement values for the concentrations of the ingredient; - measuring spectra of the individual samples with a spectrometer selected by way of example from the structurally identical spectrometers; - determining a preliminary regression model in which amplitude values of the measured spectra form the independent variables and in which the reference measurement values of the concentrations of the ingredient form the dependent variable; - selecting at least one spectrum from the measured spectra and/or an average spectrum formed from the measured spectra according to a suitability for predicting the concentration of the ingredient; - simulating tolerances of components of structurally identical spectrometers multiple times with a mathematical model of structurally identical spectrometers to obtain a multiplicity of error spectra; - adding the individual error spectra respectively to the selected spectrum or to the individual selected spectra to obtain simulated spectra; - applying the preliminary regression model to the simulated spectra to obtain in each case a prediction value for the concentration of the ingredient; - selecting a number of the simulated spectra, wherein the prediction values obtained for the selected simulated spectra depict a variation of the prediction values obtained for the simulated spectra; and - determining a resulting regression model in which amplitude values of the measured spectra and the selected simulated spectra form the independent variables and in which the reference measurement values of the concentrations of the ingredient form the dependent variable.