The Wheatstone Bridge is a circuit widely used in the area of electrical and electronic measurements.
Its constitution is very simple but of extreme utility. Basically it is constituted
of a set of four resistors formed as follows: two sets
of two resistors connected in series and these sets connected in parallel. See Figure 06-01 and Figure 06-02
where we can see two typical circuits of this system that appear in the technical literature.

This circuit is widely used on basis for temperature measurements,
resistance, mechanical resistance, balances, etc. The basic principle is
linked to the fact that the bridge can be in the state called "equilibrium", that is,
the potential difference that appears between the points a - b is
ZERO. In this case, no current will flow through the ammeter represented in these
figures by the capital letter A (in red). For this condition to be true
the following equation eq. 06-01 must be satisfied:

Observe in the figures above that in order to achieve equilibrium
of the Wheatstone bridge we use the variation of R_{2}. Naturally
that any resistance of the circuit can be used for such purpose.