Note 1 to entry: The value of the attenuation has been chosen so that the meteorological optical range provides an approximate measure of the commonly used concept of meteorological visibility.

Note 2 to entry: The meteorological optical range, v, is related to the atmospheric transmissivity, T, assumed to be uniform, by the formula

${\displaystyle v=d_0\frac{\log \mathrm{0,05}}{\log T}}$ or $T={\mathrm{0,05}}^{d_{\text{0}}/v}$

where d₀ is the length specified in the definition of atmospheric transmissivity.

These formulae are sometimes written

${\displaystyle v=\frac{\log \mathrm{0,05}}{\log T}}$ or $T={\mathrm{0,05}}^{1/v}$

with d₀ set to unity.

Note 3 to entry: This entry was numbered 845-11-20 in IEC 60050-845:1987.