Note 1 to entry: Since
Note 2 to entry: For two elementary areas d
Note 4 to entry: The mutual exchange coefficient is expressed in square metre (m2).
Note 5 to entry: This entry was numbered 845-09-71 in IEC 60050-845:1987.
Note 6 to entry: This entry was numbered 17-797 in CIE S 017:2011.