Ammeters and Voltmeters

Galvanometers, ammeters, and voltmeters :

The torque on a current loop in a magnetic field provides the basic principle of the galvanometer, a sensitive current-measuring device. A needle is affixed to a current coil—a set of loops. The torque gives a certain deflection of the needle, which is dependent upon the current, and the needle moves over a scale to allow a reading in amperes.

An ammeter is a current-measuring instrument constructed from a galvanometer movement in parallel with a resistor. Ammeters are manufactured to measure different ranges of current. A voltmeter is constructed from a galvanometer movement in series with a resistor. The voltmeter samples a small portion of the current, and the scale provides a reading of potential difference—volts—between two points in the circuit.

Hope the above explanation helped you.