The ambient conditions in the test facilities, the dynamometer characteristics, and the test drivers influence the formation of the components in vehicular exhaust gas emissions. To quantify the specific effects a standard test vehicle which is equipped with a mechanized driver and a measuring system is used as a calibrating instrument.
Variations of the barometric pressure were found to influence the exhaust test results significantly. Systematic errors up to a factor of two may be caused by malfunctions of apparently well-adjusted dynos. Furthermore, the drivers can create large deviations without violating the tolerances of the driving schedule.