where:
%Sannual = annual average sulfur content of the fuel burned during the year by the unit, as a percentage by weight;
%Sn = sulfur content of the nth sample of the fuel delivered during the year to the unit, as a percentage by weight;
Vn = volume of the fuel in a delivery during the year to the unit of which the nth sample is taken, in standard cubic feet; or, for fuel delivered during the year to the unit continuously by pipeline, volume of the fuel delivered starting from when the nth sample of such fuel is taken until the next sample of such fuel is taken, in standard cubic feet;
dn = density of the nth sample of the fuel delivered during the year to the unit, in lb per standard cubic foot; and
n = each sample taken of the fuel delivered during the year to the unit, taken at least once for each delivery; or, for fuel that is delivered during the year to the unit continuously by pipeline, at least once each quarter during which the fuel is delivered.
40 C.F.R. §72.7