Measurement and Instrumentation
A Manganin swap resistance is connected in series with a moving coil ammeter consisting of a milli ammeter and a suitable shunt in order to

 Minimize the effect of stray magnetic fields.
 Obtaine large deflecting torque.
 Reduce the size of the meter.
  Minimize the effect of temperature variation.

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Measurement and Instrumentation
For power measurement of three phase circuit by two wattmeter method, when the value of power factor is less than 0.5 lagging

Both give the same readings
One of the wattmeters will read zero
Pressure coil of the wattmeter will become ineffective.
One of the wattmeter connections will have to be reversed

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