While galvanometers useful are use ful in laboratory measurement extremely small currents,they are not portable, compact, and rugged enough for use in military equipment. a modern meter movement is used to the principle of the galvanometers but it is portable, compact, rugged, and easy to read. the coil is mounted on a shaft fitted to between two permanently-mounted jewel bearings. to indicate the amount of current flow a lightweight pointer is attached to the coil and turns with the coil.

Balance spring on each end of the shaft exerts opposite turning force on the coil and, by adjusting the tension of one spring, the meter pointer may be adjusted to be zero on the meter scales. since temperature change affected both coil springs equally, the turning effect of the springs on the meter coil is canceled out. as the meter coil turns, one spring tightens to provide a retarding force, while the author spring releases its tension. in addition to providing tension, the spring uses to carry current from the meter terminals through the moving coil.

In order that the turning force will be an increase uniformly as the current increase , the horseshoes magnet poles are shaped to the poles are shaped to form semi-circles. this brings the coil as near as possible to the north and south poles of the permanent magnet. the amount of current required to turn the meter pointer the full-scale deflection depends upon the magnet strength and the number of turns of the wire in the moving coil.

How to meter range is changed:-

Meter ranges could be changed by using a magnet of different strengths or by changing the number of turns in the coil since either of these changes would alter the amount of the current needed for the full-scale deflection. however, the wire used in the coil must always be large enough to carry the maximum current of the range of the meter is intended for, and therefore changing the wire size would only be practical in the small meter range, it is impractical to change the magnet or the coil each time the range the change. 

For measuring a large current by low range meter is used with a shunt which is a heavy wire that is a connection across the meter terminals to carry most of the current. this shunt allowed only a small part of the current to actually flow through the meter coil. usually, 0-1 milliampere meter is used, with proper size shunt connected across its terminals to achieve the discharge range.