I know I (line) and O (circle) symbols are used to specify a switch that turn on and off the power supply.
My question is What is its origin?
Because I thought that it represent a power line that can be plugged (on symbol) and a closed line (and thus without power supply) but seen that in Wikipedia said that it can come from 1 and 0 used in binary to represent on and off bits, I don't know what is the correct answer.
Note: In Wikipedia, it didn't have verified sources, so I need other source.