Method for sample-appropriate measurement using a mobile constituent analysis system comprising a housing with a window, an interface for an external reference unit and a display and operating unit, wherein a light source, an optical spectrometer, a camera, an internal reference unit and an electronic control unit are arranged in the housing, wherein the method comprises the following steps: - selecting a calibration product suitable for a sample to be examined, the said calibration product being a measurement and evaluation regime stored in a memory of the electronic control unit, the said measurement and evaluation regime calculating one or more constituents of the sample to be examined from reflection spectra captured by means of the spectrometer on the basis of a calibration model, likewise stored in the memory, and further processes for recording measurement values in sample-appropriate fashion contained in the memory; - checking the plausibility of the chosen calibration product, wherein, if the chosen calibration product does not fit to the sample within predetermined tolerance ranges, an incorrect selection is signalled and a renewed selection of an alternative calibration product is initiated, wherein, for the plausibility check of the chosen calibration product, images of the sample taken by the camera are compared with comparison images stored in a memory of the control unit for the selected calibration product; - outputting measurement conditions to be observed, which comprise at least the measurement point to be chosen and the measurement duration, depending on the selected calibration product; - capturing measurement values at the sample using the spectrometer under the measurement conditions and whilst simultaneously monitoring the measurement conditions; - processing the captured measurement values by the electronic control unit, wherein each measurement value that has been captured in compliance with the measurement conditions is declared valid; - outputting at least the measurement values found to be valid to the display and operating unit and/or another output or storage element. - selecting a calibration product suitable for a sample to be examined, the said calibration product being a measurement and evaluation regime stored in a memory of the electronic control unit, the said measurement and evaluation regime calculating one or more constituents of the sample to be examined from reflection spectra captured by means of the spectrometer on the basis of a calibration model, likewise stored in the memory, and further processes for recording measurement values in sample-appropriate fashion contained in the memory; - checking the plausibility of the chosen calibration product, wherein, if the chosen calibration product does not fit to the sample within predetermined tolerance ranges, an incorrect selection is signalled and a renewed selection of an alternative calibration product is initiated, wherein, for the plausibility check of the chosen calibration product, images of the sample taken by the camera are compared with comparison images stored in a memory of the control unit for the selected calibration product; - outputting measurement conditions to be observed, which comprise at least the measurement point to be chosen and the measurement duration, depending on the selected calibration product; - capturing measurement values at the sample using the spectrometer under the measurement conditions and whilst simultaneously monitoring the measurement conditions; - processing the captured measurement values by the electronic control unit, wherein each measurement value that has been captured in compliance with the measurement conditions is declared valid; - outputting at least the measurement values found to be valid to the display and operating unit and/or another output or storage element.