When spectrophotometry is conducted in the presence of unavoidable stray radiation, the usual expression for the absorbance [<i>A</i> =log(100/<i>T</i>)] becomes log[(100-<i>k</i>)/(<i>T</i>-<i>k</i>)], where <i>T</i> is the percent transmittance (100<i>I</i>/<i>I</i><sub>0</sub>) and <i>k</i> is the percent stray radiation. To meet the demands of routine infra-red spectrophotometry in the 15–22µ-region, a table of values of this function was prepared for 1<<i>T</i><99 and 0.5<<i>k</i><20. The calculation of these values was performed by punched card machines.
ASCHER OFLER, "Spectrophotometry in the Presence of Stray Radiation: A Table of Log[(100 - k)/(T - k)]," J. Opt. Soc. Am. 40, 401-401 (1950)