Usually made of wood, metal, or plastic, a ruler is a measuring stick. Most rulers have a straight edge used for drawing straight lines and measuring lengths. The simplest and most well-known ruler has small scales, measured in terms of inches (and/or centimeters).

In order to read a ruler, the user needs to know the main divisions. For example, when looking at a foot ruler, the longest increments are represented by inches and are usually numbered 1 through 12; the measurement starts on the left end of the ruler, which may or may not be marked with a “0.” The next divisions, from smallest to largest, are: The distances between the smallest increments represent a sixteenth of an inch, the distances between the next largest increments represent an eighth of an inch, the next represent a fourth of an inch; and, finally, a half of an inch. (For more about measurement, see “Mathematics throughout History.”)