Measuring electric voltage. Circuit diagram showing the arrangement of equipment used to measure the voltage (potential difference) in an electrical circuit. The components are represented by standard symbols. At upper left is a battery consisting of one cell; an open switch is at lower left; a resistor is at centre; and a voltmeter is at right. When the switch is closed, the potential difference (voltage) of the battery will cause electric current to flow round the circuit. The value of the electric current will vary depending on the value of the resistor. The voltmeter is used to measure the difference in electric potential (the voltage) between two points in the circuit. Here, it has been connected 'across' the resistor, thus measuring the voltage across the resistor due to the battery.