I’ve been reading a lot about paper sizes, qualities, textures for various things I’m thinking about for the library. I had no idea what all the numbers stood for – A4, A1, A???. Here’s a chart just in case you were wondering too. From Papersizes.org.
Jack Of All Trades 
Since I’ve become a huge fan of the Midori Traveler’s Notebook, and of course, European notebooks in general, I’ve wondered what size is what. This was so interesting! In my classroom, we just say “loose leaf notebook paper” which isn’t nearly so exact. 😉