40 CFR 89.416 - Raw exhaust gas flow.
The exhaust gas flow shall be determined by one of the methods described in this section and conform to the tolerances of table 3 in appendix A to subpart D:
(a) Measurement of the air flow and the fuel flow by suitable metering systems (for details see SAE J244. This procedure has been incorporated by reference. See § 89.6.) and calculation of the exhaust gas flow as follows:
(b) Exhaust mass calculation from fuel consumption (see § 89.415) and exhaust gas concentrations using the method found in § 89.418.