The Wheatstone Bridge consists of two
resistive potential dividers connected to a common
voltage source. If one potential divider has resistances
R1 and R2 in series
and the other potential divider has resistances R3
and R4 in series, with R1
and R3 connected to one side of the
voltage source and R2 and R4
connected to the other side of the voltage source, then
at the balance point where the two resistively divided
voltages are equal:
R1 / R2 = R3
/ R4
If the value of resistance R4
is unknown and the values of resistances R3,
R2 and R1 at the
balance point are known, then:
R4 = R3R2
/ R1
