Square centimeter is a common unit for mathematical calculation and area. The symbol is cm2, which is the metric unit of area, and it is defined as "the area of a square with a side length of 1 cm". About the size of a thumb nail.

Mask is a sanitary and epidemic prevention product, which is usually worn on the nose and mouth to filter the air entering the nose and mouth to block harmful gases, smells, droplets, viruses and other substances. It is made of gauze or paper.