Measurement and Instrumentation
A resistance is measured by the voltmeter-ammeter method employing dc excitation and a voltmeter of very high resistance connected directly across the unknown resistance. If the voltmeter and ammeter reading are subject to maximum possible errors of ± 2.4 % and ± 1.0 % respectively, then the magnitude of the maximum possible percentage error in the value of resistance deduced from the measurement is nearly

 ± 1.4%
 ± 3.4%
 ± 1%
 ± 2.4%

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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

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

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