The invention relates to a method for true-to-sample measurement by means of a mobile ingredient analysis system, which comprises: a housing having a window； an interface for an external reference unit； a display and operating unit； a light source； an optical spectrometer； a camera； an internal reference unit； and an electronic control unit. The method comprises the following steps: selecting a calibration product suitable for a sample to be examined； performing a plausibility check of the selected calibration product, an incorrect selection being signaled and a new selection of an alternative calibration product being initiated； outputting measurement conditions to be met, which comprise the measurement point to be selected and the measurement duration, in accordance with the selected calibration product； capturing measured values of the sample by means of the spectrometer under the measurement conditions and with simultaneous monitoring of the measurement conditions； processing the captured measured values by means of an electronic control unit, each measured value that was captured while the measurement conditions were met being declared valid； outputting at least the measured values deemed valid at the display and operating unit or to another output or storage element.
