To measure with a ruler the most important thing to do is put the end of the ruler with the 0 exactly at the end of whatever you are measuring. Then you look at the other end of the object you are measuring and see where it stops on the ruler. The larger numbers stand for inches (or centimeters). Inches can be broken down into 1/2′, 1/4′, 1/8′ and 1/16′. On a centimeter ruler the smallest lines are millimeters. There are 10 mm to a centimeter.