One Thing I'm Collecting: obscure fact for the day

Something I'm collecting for a very long term project are squares of cotton material which are at least 6 inches square, ideally slightly larger. Any colour or pattern.

On a completely differnt note, I've been reading about Copernicus' book De Revolutionibus. This is the book that first proposed the heliocentric solar system, with the Earth and planets circling the Sun.

No, I haven't been reading about the contents of the book, I've been reading about the book itself. It was printed on a paper size known as pot paper, with sheets that are 399mm x 282mm. Those who are capable of incredibly fast calulations will already have spotted that this is the ratio √2 : 1 . The useful thing about this ratio is that if you fold the paper in half, the length of the sides still has the same ratio.

Getting slightly less obscure, this ratio is still in use today as one of the defining features of the A series of paper. An A4 sheet of paper folded in half makes an A5 sheet. Anyone who has used this knows just how useful this ratio is: you can photocopy two sheets of A4 onto one sheet of A3, etc.

(The other defining feature of the A series is that A0 has an area of 1 meter². A4 is the European equivalent of US letter size.)