Where:
xidriftcorrected = concentration corrected for drift.
xrefzero = reference concentration of the zero gas, which is usually zero unless known to be otherwise.
xrefspan = reference concentration of the span gas.
xprespan = pre-test interval gas analyzer response to the span gas concentration.
xpostspan = post-test interval gas analyzer response to the span gas concentration.
xi or x = concentration recorded during test, before drift correction.
xprezero = pre-test interval gas analyzer response to the zero gas concentration.
xpostzero = post-test interval gas analyzer response to the zero gas concentration.
Example:
xrefzero = 0 [MICRO]mol/mol
xrefspan = 1800.0 [MICRO]mol/mol
xprespan = 1800.5 [MICRO]mol/mol
xpostspan = 1695.8 [MICRO]mol/mol
xi or x = 435.5 [MICRO]mol/mol
xprezero = 0.6 [MICRO]mol/mol
xpostzero = -5.2 [MICRO]mol/mol
xidriftcorrected = 450.2 [MICRO]mol/mol
xprespan
xprezero
40 C.F.R. §1065.672