https://doi.org/10.1351/goldbook.D01536
The negative decadic logarithm of one minus @A00035@ as measured on a uniform sample: \[A=- \log _{10}(1- \alpha )\]
Source:
PAC, 1985, 57, 105. (Names, symbols, definitions and units of quantities in optical spectroscopy (Recommendations 1984)) on page 116 [Terms] [Paper]