The unit siemens for the conductance G is defined by where Ω is the ohm, A is the ampere, and V is the volt.
NIST's Guide for the Use of the International System of Units (SI) refers to the mho as an "unaccepted special name for an SI unit", and indicates that it should be strictly avoided.
[5][clarification needed] The SI term siemens is used universally in science and often in electrical applications, while mho is still used in some electronic contexts.
The usual typographical distinctions (such as italic for variables and roman for units) are difficult to maintain.
Likewise, it is difficult to distinguish the symbol "S" (siemens) from the lower-case "s" (seconds), potentially causing confusion.