points from the analyzers a further step of using a precalibrated or linear analyzer such as the flame ionization detector of the system to accurately determine the percentage ratio of intermediate divide points obtained by mixing various amounts of zero gas with the span gas simplifies the calibration procedure and eliminates the need for an expensive gas divider application_number US 29363094 A description referring now to the drawings in detail numeral 10 generally indicates the gas flow system of an emission analysis bench 12 used for testing the tailpipe exhaust emissions of automotive vehicles it should be understood however that the invention could as well be applied to other types of emission analysis benches such as bag engine out and intermediate types in addition to tailpipe emission analysis benches as seen in fig1 the bench 12 mounts four distinct emission analyzers an fid flame ionization detector analyzer 14 an nox analyzer 16 a co analyzer 18 and a co2 analyzer 20 the fid analyzer 14 serves in operation to measure the concentration of hydrocarbons hc in samples of vehicle exhaust supplied to the system 10 similarly the nox analyzer measures the concentration of nitrogen oxides the co analyzer measures the concentration of carbon monoxide and the co2 analyzer measures the concentration of carbon dioxide in the vehicle exhaust.