Siemens (unit) - Mho

"Mho" redirects here. It is not to be confused with Mohs (disambiguation).

Mho is an alternative name of the same unit, the reciprocal of one ohm. Mho is derived from spelling ohm backwards and is written with an upside-down capital Greek letter Omega:, Unicode symbol U+2127 (℧). According to Maver the term mho was suggested by Sir William Thomson. The mho was officially renamed to the siemens, replacing the old meaning of the "siemens unit", at a conference in 1881.

The term siemens, as it is a SI term, is used universally in science and often in electrical applications, while mho is still used primarily in electronic applications. Two reasons are usually given for using mho instead of siemens in electronic applications:

• The inverted Omega and the mho, while not an official SI abbreviation, has the advantage of being less likely to be confused with a variable than the letter S when doing algebraic calculations by hand, where the usual typographical distinctions (such as italic for variables and Roman for unit names) are difficult to maintain. Likewise, it is difficult to distinguish the symbol S from the lower case s where second is meant, potentially causing confusion.
• The term siemens could be confused with the large multinational electronics company Siemens.