A Wheatstone bridge is specifically designed for the accurate measurement of small and unknown resistances. It operates on the principle of balancing two legs of a bridge circuit, enabling precise determination of resistance values.

Potentiometer: Used to measure potential difference or electromotive force (emf), not to measure resistance directly.

Rheostat: A variable resistor utilized to control current, rather than for measuring resistance.

Wheatstone Bridge: The most effective method for measuring very small resistances.