Post office box (electricity)

The post office box was a Wheatstone bridge–style testing device with pegs and spring arms to close electrical circuits and measure properties of the circuit under test.

[1][2] The boxes were used in the United Kingdom by engineers from then General Post Office, who were responsible for UK telecommunications to trace electrical faults, i.e. to determine where a break occurred in a cable which could be several miles in length.

Post office boxes were common pieces of scientific apparatus in the UK O-Level and A-Level schools public examination physics syllabus in the 1960s.

Coils of wire are wound non-inductively, mounted in the body of the box, and have a negligible temperature coefficient.

You can help Wikipedia by expanding it.This history of science article is a stub.