Potential difference is measured by means of:

Potential difference is the scientific term for electromotive force, more commonly known as voltage. It represents the electrical pressure that drives current through a circuit. Because it is measured in volts, the correct instrument to measure it is a voltmeter. The distractors represent tools for measuring other fundamental electrical properties. An ammeter measures current (amperes), an ohmmeter measures resistance (ohms), and a wattmeter measures electrical power (watts).