內部結構of ammeter and voltmeter

Traditional ammeter and voltmeter is made up by different combination of connection of moving coil galvanometer and resistor.

Structure of galvanometer :
http://en.wikipedia.org/wiki/Galvanometer

To make an ammeter , you should add a resistor in parallel to the galvanometer(this resistor is called "Shunt")

To make a voltmeter, you should add a resistor in series to the galvanometer (this resistor is called "multiplier")