Meter bridge: A 1-meter uniform wire replaces two arms of the Wheatstone bridge. Unknown resistance X = R * $\frac{l}{100-l}$, where l is the balancing length. End corrections may apply if junctions have resistance. Most accurate when l is near 50 cm (balanced sensitivity).

Potentiometer: A long uniform wire carrying steady current. Potential is proportional to length: V = kl where k = $\frac{V_0}{L}$ is the potential gradient. Comparing EMFs: $epsilon_1$/$epsilon_2$ = $\frac{l_1}{l_2}$ (null method — no current drawn from the cell). Internal resistance: r = R($l_1$/$l_2$ - 1), where R is external resistance across the cell, $l_1$ is open-circuit balance, $l_2$ is with R connected. Advantage over voltmeter: measures true EMF (not terminal voltage), infinite effective resistance.