Determining resistances using a Wheatstone bridge

In the experiment P3.2.3.4, a voltage U is applied to a 1 m long measuring wire with a constant cross-section. The ends of the wire are connected to an unknown resistor R_x and a variable resistor R arranged behind it, whose value is known precisely. A sliding contact divides the measuring wire into two parts with the lengths s₁ and s₂. The slide contact is connected to the node between R_x and R via an ammeter which is used as a zero indicator. Once the current has been regulated to zero, the relationship

applies. Maximum accuracy is achieved by using a symmetrical experiment setup, i. e. when the slide contact over the measuring wire is set in the middle position so that the two sections s₁ and s₂ are the same length.