Abstract: A method for the direct presentation of a differential measured quantity, in particular, a differential gas concentration measurement, in terms of its correct physical unit is disclosed. A characteristic curve representing the output of a gas sensor detector as a function of gas concentration is obtained in an absolute coordinate system. A reference level at which the differential measurement is to occur is defined on this characteristic curve by a defined input or, respectively, output value. This reference level defines the origin of a differential coordinate system from which the differential measurement may be directly ascertained.