Place the "0" mark on the end of the ruler next to one end of the length you are measuring. Be careful, because on some rulers the "0" mark does not begin exactly at the edge of the ruler.
Extend the ruler along the length of the object you are measuring.
Determine the length of the object by reading the markings on the ruler. Each large mark represents one inch, while each smaller mark represents 0.1 inches. So if your object ends three small marks past the 7-inch mark, the length is 7.3 inches.