During the last ballot round before publication of D8290 in December 2020, a commenter stated, that the definitions of I0 and I do not match the typical textbook definitions and that equation (1) will yield negative absorbance as defined in the test method. This ballot proposes to correct this oversight.
The automated data analysis of the equipment required to run the test method has always been done according to the definitions proposed in this ballot. I.e., all data published in RR D02-2012 has been calculated from positive absorbances.
Furthermore, it is important to note, that using either set of definitions would lead to identical test results obtained from equation (2), as long as the calibration curve was calculated from data using the same definitions in equation (1). The slope and intercept of the calibration would be different, but the sign flip would cancel out when calculating the FAME concentration using equation (2).
Additionally, it was suggested to add a delta to the absorbance in Equation (1) and (2) to exemplify that the test method uses the difference of the absorbance measured at two wavenumbers instead of using absorbance measured at one wavenumber