Absorbance calculated with logarithm base
\(e\) (natural or Napierian logarithm).
Note:
Confusion with the decadic absorbance must be avoided.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 667 (https://doi.org/10.1515/pac-2019-0203)