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.
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. (en)
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. (en)