transmittance optical density
logarithm to base 10 of the reciprocal of the transmittance,
Note 1 to entry: The transmittance optical density has unit one.
Note 2 to entry: This entry was numbered 845-04-66 in IEC 60050-845:1987.
Note 3 to entry: This entry was numbered 17-843 in CIE S 017:2011.