I did not know this.
Some bright spark somewhere thought that there should be a universal icon for ‘ON’ / ‘OFF’ switches. He or they (possibly a group of time on their hands boffins), decided that all of the world should be familiar with ‘BINARY CODE’. Binary code works with zeros and ones. Zero for being non-active and one for being active. So we have 0 for OFF and I for being ON. Some of these switches have lamps in them which make life easier.
Anyone also funny I did not know thats?
There are only 10 types of people who understand binary - those who do and those who don’t.
Thank you for the information. I fall into the didn’t know that category.
I get it now after after decades of being confused.
First learning of the day.
Why do so many smartphones and websites have cryptic icons.
I know it’s common now but this one used to drive me potty:
It could also be In and Out… Seeing it from electricity’s perspective 
Would it be “In or maybe out” if the electricky were DC?
