Consider a wheatstone bridge. Suppose a resistance Rx is istalled as the unknown, and the bridge is balanced giving a potentiometer divider ratio S_o. Now leave the potentiometer alone but let the unknown resistance change by a small amount DeltaRx. Show that the unblanced potential diference is
DeltaV = E(DeltaRx/Rx)(1 - S_o)*S_o
E is the voltage running into the circuit from the voltage source