Hi,
Electrical voltage and current are two quantities in an electrical circuit. The voltageis measured across a branch of a circuit. The device that measures the voltage is the voltmeter. Direct current is the unidirectional flow of an electric charge. The principle behind measurement of dc voltage and dc current is as follows Voltmeter is a voltage meter. Which measures the voltage between the two nodes. We know the unit of potential difference is volts. So it is a measuring instrument which measures the potential difference between the two points.