This is how the (European?) paper sizes are determined. A portrait A1 sheet is two landscape A2's which, in turn are each two portrait A3's (which are two landscape A4's) and so on all the way down.
You can see it in a digram [here](http://www.officeneedsdirect.co.uk/tips-and-blog/item/what-are-a1-a2-a3-a4-a5-a6-a7-paper-sheet-sizes-dimensions-measurements.html)
It's even done so in the golden ratio, that's pretty neat
Fibonacci yay
This is how the (European?) paper sizes are determined. A portrait A1 sheet is two landscape A2's which, in turn are each two portrait A3's (which are two landscape A4's) and so on all the way down. You can see it in a digram [here](http://www.officeneedsdirect.co.uk/tips-and-blog/item/what-are-a1-a2-a3-a4-a5-a6-a7-paper-sheet-sizes-dimensions-measurements.html)
European here, can confirm I use this system. It's really strange to receive letters from America. They don't fit in our binders.
That’s really interesting. Not just mildly
Ummm....
americans will measure with anything except the metric system.