decadic absorbance, A

https://dx.doi.org/10.1351/goldbook.D01536
The negative decadic logarithm of one minus absorptance as measured on a uniform sample:
A = − log 10 ( 1 − α )
Source:
PAC, 1985, 57, 105 (Names, symbols, definitions and units of quantities in optical spectroscopy (Recommendations 1984)) on page 116