[1][2][3] The reference values for each type of quantity are often specified by international standards.
Power and field levels are used in electronic engineering, telecommunications, acoustics and related disciplines.
Field levels are used for voltage, current, sound pressure.
[6] The neper, bel, and decibel are related by[7] Level and its units are defined in ISO 80000-3.
This is motivated by simplifying the expressions involved, as in systems of natural units.