Area unit: square nanometer, square micrometer, square millimeter (mm? ), square centimeter (cm? ), square decimeter (dm? ), square meters (m? ), square kilometers (km? )
Length ratio: mm to cm, cm to decimeter, decimeter to meter, the ratio is10; The speed from meters to kilometers is 1000.
Area permeability: from millimeter to millimeter, from millimeter to bisection, from bisection to square meter, permeability100; The ratio of each square meter to each square meter is 1000000.
Say with your hands ~ is it all? ......