Abstract: Especially precise and reliable measurements and evaluations are obtained by measuring one or more propagation parameters of electromagnetic waves in a wave guide or resonator at least partially filled with fuel and evaluated in an evaluating circuit as the measure for the alcohol content and/or the calorific value. According to one embodiment, the travel time or the travel time difference of an electromagnetic wave between two or more points in a wave guide filled with fuel is determined and is evaluated through computer or circuit technology as the measure for the alcohol content and/or the calorific value.