Siemens (unit)

The siemens, abbreviated S, is the SI unit of electrical conductance. It is the conductance which will allow a current of one ampere across a potential drop of one volt. The siemens is the reciprocal of the ohm.

The siemens is named for Ernst Werner von Siemens (1816 - 1892), an early pioneer in electrical engineering, and the founder of what has become Siemens AG, a large electrical and electronics firm.

The siemens is a derived unit in the SI, equal to 1 A/V, or Ω-1; or in terms of SI basic units: V = s3·A2·m-2·kg-1.

Siemens and mho
Before the BIPM approved the siemens as a derived unit in 1971, the common unit for conductance was the mho (ohm spelled backwards), abbreviated ℧. The mho is still in use, despite not having official status, as the upside-down omega is not likely to be confused with lower-case s for seconds, nor for S occurring in formulas.