Carey Foster bridge
![The Carey Foster bridge. The thick-edged areas are busbars of almost zero resistance.](/Images/godic/202501/03/Carey_Foster_bridge.svg4312.png")
![A standard Wheatstone bridge for comparison. Points A, B, C and D in both circuit diagrams correspond. X and Y correspond to R1 and R2, P and Q correspond to R3 and RX. Note that with the Carey Foster bridge, we are measuring R1 rather than RX.](/Images/godic/202501/03/Wheatstonebridge.svg4312.png")
In electronics, the Carey Foster bridge is a bridge circuit used to measure low resistances, or to measure small differences between two large resistances. It was invented by Carey Foster as a variant on the Wheatstone bridge. He first described it in his 1872 paper "On a Modified Form of Wheatstone's Bridge, and Methods of Measuring Small Resistances" (Telegraph Engineer's Journal, 1872–1873, 1, 196).