What is AVO meter?

The AVO meter stands for ampere, volt, and ohmmeter. The ammeter, voltmeter and ohmmeter all use a basic D.Arsonval  movement. The difference between these instruments is the circuit in which the basic movement is used. It is therefore obvious that an instrument can be designed to perform these three measurement functions.The instrument which contains a function switch to connect the appropriate circuits to the D.Arsonval movement is called a multimeter or AVO meter.

This is multi purpose instrument as it indicates, it is used for measurement of current (d.c and a.c), voltage (d.c and a.c) and resistance. With the external source, high resistance above (1m ohm), inductance and capacitance can also be measured with this instrument.
Construction And Working:
The of the meter consists of a dc moving coil instrument taking very low current of the order of 1mA for full scale deflection. On dc a tapped universal shunt is used for current measurement and a tapped series resistance for voltage measurements. On ac a transformer feeds into a metal rectifier, the output from which goes to the dc movement. Thus the same scales are used for dc and ac battery to the resistance under test measuring the resultant current. Since the resultant current is by "Ohm's Law", inversly proportional to the resistance, so the scale can be calibrated directly in Ohms, Kilo and mega-ohms.