Measurement and Instrumentation
Electrostatic instruments are normally used for

High voltage measurements
High current measurements
Low current measurements
Low voltage measurements

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

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