The Wheatstone Bridge is designed to enable the calculation of unknown resistances. It is very accurate, and works on reducing the potential difference or current between A and B to zero. It is much easier and more accurate to change the variable resistor
and estimate when the current is zero than to measure the voltage across a resistor, the current though a resistor then use the equation
Having obtained a zero reading on the resistor, the unknown resistance R-x could then be calculated becauseand
are in the same ratio as
and
Hence
We rearrange this to make
the subject: