A constant, full-air-conditioned quantity of humidity- and/or temperature-conditioned combustion gas, such as air, is supplied to the combustion engine at each time-point. This quantity is at least as large as the maximum quantity required by the engine. Unneeded gas is fed to a CVS full-flow system. A predetermined desired pressure value for the combustion gas is adjusted upstream of the CVS full-flow system and also upstream of the conditioning of the combustion gas. An independent claim is included for an apparatus for exhaust gas measurement in an engine test rig.