40 CFR § 86.156-98 - Calculations; refueling test.
(a) The calculation of the net hydrocarbon mass change and methanol mass change (if applicable) in the enclosure is used to determine refueling mass emissions. The mass is calculated from initial and final hydrocarbon and methanol (if applicable) concentrations in ppm carbon, initial and final enclosure ambient temperatures, initial and final barometric pressures, and net enclosure volume using the equations of § 86.143-96. For vehicles with multiple tanks, the results for each tank shall be calculated and then summed to determine overall refueling emissions.
(b) The final results for comparison with the refueling control emission standard shall be computed by dividing the total refueling mass emissions by the total gallons of fuel dispensed in the refueling test (see § 86.154-98(e)(7)(ii)).
(c) The results of all emission tests shall be rounded, in accordance with ASTM E 29-67 (reapproved 1980) (as referenced in § 86.094-28(a)(4)(i)(B)(2)(ii)) to the number of decimal places contained in the applicable emission standard expressed to one additional significant figure.