Measurement and Instrumentation
Comparison methods are used

 because they are expensive.
 because they take least time in measurement.
 because they are most simple.
 when a high accuracy of measurement is required.

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

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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

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
Both give the same readings

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