Comparision Of Emf Of Two Cells

A potential gradient is created in the wire by a standard cell for the comparision of emf's of two cells in a potentiometer experiment. Which possibility of the following will cause failure of the experiment.

The following diagram shows the circuit for the comparision of e.m.f. of the cells. The circuit can be corrected by:-

Potentiometer|Principle|Potential Gradient|Application|To Compare EMF Of Two Cell

Comparision|Summary

Comparision|Summary

How will you campare emf of two cells by potentiometer?