Resistance bridge

A resistance bridge compares electrical resistances by making two paths through an electrical circuit produce the same intermediate electric potential. The Wheatstone bridge turns this into a null measurement: adjust one arm until a detector joining the two intermediate points reads zero, then infer the unknown from a ratio. This is useful because the balance relation does not require an accurately calibrated detector gain or supply electric potential difference, provided the supply is nonzero and the resistors obey Ohm's law.