1 cm is the thickness of a math book. A book of 1 cm is about 200 ~ 300 pages. Take 70 grams of copy paper as an example. The thickness of a piece of paper is several tenths of a millimeter. The size of a math book is 2 1mm ×29.7mm according to the size standards of most countries in the world. So this centimeter can only be the thickness of a math book. It can't be any other size, let alone the thickness of a piece of paper.