A note about 'A' paper sizes:

'A' sizes are standard paper sizes, all of which have the same shape. A4 is the normal paper size used in W. Europe for most purposes, such as writing letters. It is very roughly similar to foolscap. It measures 210 mm x 297 mm (8¼ inches by 11¾ inches approximately)

The interesting thing about the 'A' shape is that when you fold it in half, the folded shape is exactly the same as the original and this is true of all the various A sizes: if you start with a sheet of A2 paper for example (the size of a fairly large layout pad) and fold it in half, you have made two sheets of A3 paper (roughly the same size as 15 field animation paper). Fold an A3 sheet in half and you have the A4 size and so on.

(OK, maybe it isn't interesting).