Siemens is in the SI unit of electrical conductance and named after Werner von Siemens. The conductance of 1 S is the reciprocal of the electrical resistance of 1 Ω, the ohm is the SI unit of electrical resistance:
1860, Siemens had published the essay proposal of a reproducirbaren resistance Maaßes in Poggendorff's Annals of Physics and Chemistry, see detail below ohms.
Mho is an obsolete term for the unit of Siemens, the name goes back to William Thomson. The term mho ( ohm spelled backwards ) and the symbol ℧ ( an upside down big Omega ) express that it is the reciprocal of the units of ohms. They were used to in the thirties of the twentieth century, in the United States in the field of electronics informally continue.