A galvanometer is a tool that measures the flow of electric charges through a wire. This basic device consists of a coil placed in a magnetic field. It can be used for detecting and comparing small electric currents.
The ideas of galvanometers are known to have developed from an observation made by Hans Orsted in 1820. He had found out that the needle of a magnetic compass deflects near a wire that has electric current passing through it. But it was Johann Schweigger who built the first sensitive galvanometer in the same year. Galvanometers, since then, came to commercial use.
A galvanometer can be used as an ammeter, as well as a voltmeter. By connecting a shunt in parallel to the coil, it acts an ammeter, and if the shunt is connected in series with the galvanometer coil, it becomes a voltmeter.