Historical
IEC 60027-2 Ed. 2.0 b:2000
Letter symbols to be used in electrical technology - Part 2: Telecommunications and electronics
Defines rules for the use and writing of symbols for general quantities, symbols for quantities concerning two-port networks, symbols for line transmissions of signals (including cables), symbols for radio wave propagation, symbols for quantities concerning waveguide propagation, symbols for aerials (antennas), symbols for electro-acoustics and symbols for equivalent circuits of piezo-electric crystals.
International Electrotechnical Commission [iec]