Background A current flows in an electrical circuit driven by the potential difference at the battery. The current and the potential drop are measured via a current flowing through a galvanometer. A galvanometer is a small coil suspended in a magnet. A change in current puts the coil in a new position. However, only a very small current can flow through this galvanometer moves the coil.
Voltage is measured by putting the galvanometer across the voltage drop to be measured.
Current is measured by putting the multimeter in the circuit itself. Thus, a voltmeter needs a high resistance to make the most accurate measurement and a ammeter a very low resistance. At the same time the current over the galvanometer has to be kept very small.