pods, cell phones, laptops, and coffeemakers; these are all items you use everyday that rely on circuits to power them. But do the batteries in your graphing calculator use the same amount of current as the milk-foamer in your espresso machine? I think not! Different circuits require different amounts of potential difference to maintain the flow of current. This potential difference is measured by a device known as a voltmeter. Before getting into the specifics about the voltmeter itself, it is important to realize what it actually measures. Electric potential can be defined as the electric potential energy per unit of charge. Since electric potential energy is measured in Joules and charge is measured in Coulombs, it can be said that 1 Volt= 1 Joule/Coulomb.