A Wheatstone bridge array, the key design element of the piezoresistive sensor technology, is a measuring instrument invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. It is used to measure an unknown electrical resistance by balancing two legs (R1 and R2 comprise one leg, and R3 and RX comprise the other) of a bridge circuit, one leg of which includes the unknown component (RX). With no pressure applied, this circuit is in balance. When the diaphragm is deflected, two resistors are subjected to tangential stress and two to radial stress, and the circuit becomes unbalanced. This results in a low level, measurable resistance change at RX (so the bridge remains balanced) that can be amplified to provide the output signal required by the application. Strain in the elastic region is proportional to stress, and the result is a very good accurate pressure measurement.