Voltmeter is an instrument that measures the voltage (difference in potential) between two points of an electric current. Most commercial voltmeters are galvanometers connected in series with a high resistance. They have scales that read in volts. A typical direct-current voltmeter has a magnet shaped like a horseshoe. To each pole (end) of the magnet is attached a semicircular piece of soft iron that also becomes magnetized. These pieces of soft iron direct the magnetic field toward a small iron cylinder placed between the poles of the magnet. Since soft iron becomes highly magnetized, this cylinder concentrates the magnetic field.