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.

ANSWER DOWNLOAD EXAMIANS APP

Measurement and Instrumentation
Potentiometer method of DC voltage measurement is more accurate than direct measurement using a voltmeter because

 It loads the circuit to maximum extent.
 It loads the circuit moderately.
 It uses centre zero galvanometer instead of voltmeter.
  It does not load the circuit at all.

ANSWER DOWNLOAD EXAMIANS APP