Note 1 to entry: The unit of length has to be specified. If a new unit of length is used that is k times the magnitude of the original one, then the value of τ_i,o(λ) will change to ${{\tau }^{\prime }}_{\text{i}\text{,o}}^{}(\lambda )={[{\tau }_{\text{i}\text{,o}}(\lambda )]}^k$.

Note 2 to entry: The spectral transmissivity has unit one.

Note 3 to entry: This entry was numbered 845-04-87 in IEC 60050-845:1987.