A combined current and potential meter. It is constructed on the general
lines of a Siemens’ Electro Dynamometer. If in it one coil is made of
coarse wire and is placed in series with the current conductor, and if
the other is wound with fine wire and is connected as a shunt from point
to point whose potential difference is to be determined, the instrument
becomes a watt meter.

Synonym–Energy Meter.