The meters which are connected in series with the circuit whose current is to be measured are called ammeters. The power loss in ammeter is I2Ra where Ra is ammeter resistance. To have low power loss, ammeter resistance must be very low.
The meters which are connected in parallel with the circuit whose voltage is to be measured are called voltmeters. The power loss in voltmeters is V2/Rv where Rv is voltmeter resistance. To have low power loss, voltmeter resistance must be very high.
The construction and working principle of both the meters is same. Both are basically current sensing devices but they have following differences :
Voltmeters, and multitesters generally, tend to be fragile instruments that can be damaged by thoughtless actions like using a voltmeter made to measure small amounts of current to measure a large voltage. However, another unwise move is to use a voltmeter intended for measuring large voltages to measure small amounts of voltage. In this scenario, although the voltmeter will not get damaged the readings one will get will not be accurate. Both extremes should be avoided.
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