A voltmeter must be connected in parallel to measure the voltage of a device because objects in parallel experience the same potential difference. A voltmeter is used to measure the electrical potential difference between two locations in an electrical circuit.
Two devices used to measure electric current and voltage are the voltmeter and ammeter. Voltmeter and ammeters can be found in some cars, digital cameras, cellphones and tuner amplifiers. A voltmeter measures the voltage of a circuit, whereas the ammeter, which gets its name from the unit for electric current, amperes, measures the current of a circuit, according to Boundless. The ammeter must be connected to a device in series because objects in a series experience the same current. The devices cannot be connected to a voltage source because ammeters are designed to work under minimal burden. Burden refers to the voltage drop across the ammeter, normally a very small fraction of a volt.
The galvanometer is an instrument that measures current flow using the movement or deflection of a needle, which is produced by a magnetic force acting on a wire that current flows through. The galvanometer is the heart of most analog meters. An analog voltmeter uses a pointer that moves across a scale according to the level of voltage and a digital would display a number.