Abstract: In a two-beam gas analyzer, a measurement beam passes through a measurement cuvette filled with a measurement gas, and a comparison beam passes through a comparison cuvette filled with a comparison gas. Using a detector arrangement, a difference signal is generated from the beams exiting from the two cuvettes resulting in a measurement value which corresponds to the measurement gas concentration when weighted with a weighting factor. To allow recalibration after a calibration of the two-beam gas analyzer with calibration gas and adjustment of the weighting factor to a value which results in the appropriate calibration value as the measurement value, without having to fill the measurement cuvette with a calibration gas, an additional factor is determined when the measurement cuvette is not filled or is filled with inert gas. Thus, the difference signal corresponds to the calibration value when weighted with the weighting factor and the additional factor.