* Standard rulers are usually marked in millimeters: Most rulers are divided into centimeters (cm), and each centimeter is further divided into 10 millimeters (mm).
* 0.4 cm is equal to 4 mm: To convert 0.4 cm to mm, multiply by 10 (since 1 cm = 10 mm): 0.4 cm x 10 = 4 mm.
So, to find 0.4 cm on a ruler, you would look for the 4 mm mark.
