voltage
21.4 DC Voltmeters and Ammeters Voltmeters measure voltage, and ammeters measure current. A voltmeter is placed in parallel with the voltage source to receive full voltage and must have a large resistance to limit its effect on the circuit. An ammeter is placed in series to get the full current flowing through a branch and must have a small resistance to limit its effect on the circuit. Both can be based on the combination of a resistor and a galvanometer, a device that gives an analog reading of current. Standard voltmeters and ammeters alter the circuit being measured and are thus limited in accuracy.