Measurement and Instrumentation
In DC potentiometer measurments, a second reading is often taken after reversing the polarities of the DC supply and the unknown voltage and the average of the two reading is taken. This is with a view of eliminate the effects of

 Ripples of the DC supply.
 Errorneous standardisation.
 Stray magnetic fields.
  Stray thermal emfs.

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Measurement and Instrumentation
Which of following is not correct?

  An electronic voltmeter draw appreciable current from the source.
 An ammeter should have a very low resitance.
 Voltmeter should have very high resistance.
 A shunt should have a very low resistance.

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