A calibration method for calibrating a camera for detecting an analyte in a sample , comprising: a. providing a set of color coordinate systems, the set of color coordinate systems comprising a plurality of different color coordinate systems configured for describing a color of an object; b. providing a set of test samples having known concentrations of the analyte; c. applying the test samples to a set of test elements , each test element having at least one test field comprising at least one test chemical configured for performing an optically detectable detection reaction with the analyte, thereby creating at least one colored test field for each of the test samples ; d. acquiring images of the colored test fields by using the camera ; e. generating color coordinates for the images of the colored test fields , by using the color coordinate systems of the set of color coordinate systems, thereby creating a set of color coordinates for the test samples and for the color coordinate systems; f. providing a set of coding functions, the set of coding functions comprising a plurality of coding functions for transforming color coordinates of a test field into a corresponding concentration of the analyte in the sample; g. transforming the set of color coordinates generated in step e. into a set of measured concentrations by using the set of coding functions; and h. comparing the set of measured concentrations with the known concentrations of the test samples of the set of test samples and determining a best match color coordinate system of the set of color coordinate systems and a best match coding function of the set of coding functions for which the set of measured concentrations best matches with the known concentrations. a. providing a set of color coordinate systems, the set of color coordinate systems comprising a plurality of different color coordinate systems configured for describing a color of an object; b. providing a set of test samples having known concentrations of the analyte; c. applying the test samples to a set of test elements , each test element having at least one test field comprising at least one test chemical configured for performing an optically detectable detection reaction with the analyte, thereby creating at least one colored test field for each of the test samples ; d. acquiring images of the colored test fields by using the camera ; e. generating color coordinates for the images of the colored test fields , by using the color coordinate systems of the set of color coordinate systems, thereby creating a set of color coordinates for the test samples and for the color coordinate systems; f. providing a set of coding functions, the set of coding functions comprising a plurality of coding functions for transforming color coordinates of a test field into a corresponding concentration of the analyte in the sample; g. transforming the set of color coordinates generated in step e. into a set of measured concentrations by using the set of coding functions; and h. comparing the set of measured concentrations with the known concentrations of the test samples of the set of test samples and determining a best match color coordinate system of the set of color coordinate systems and a best match coding function of the set of coding functions for which the set of measured concentrations best matches with the known concentrations. <EOS>