SSC JE Electrical Engineering 2011 Paper

The compensating coil is connected in series with the pressure coil circuit and is made nearly identical to the current coil. The current coil and compensating coil carry current of $\left(\mathit{I}+{\mathit{I}}_{\mathit{P}}\right)$ and IP Respectively, and they produce field corresponding to these current. The compensating coil is so connected that it opposes the field of current coil. Thus the resultant field is due to current I only. Hence the error dye to pressure coil current following in current coil.