Abstract
Breath test analysers are either not calibrated at all or calibrated with liquid simulators during their operational period of use. Depending on the stability in time of the instruments, calibration intervals can be as long as a month. For evidential tests there is a higher demand on the stability of the calibration then based on a scientific approach. Better calibration techniques are only possible if new preparation methods become available. A number of these methods are outlines showing the quality of the gas mixtures and the comparisons with the exciting method.