On a miter saw, when you're cutting a 90 degree cut, the miter saw reads zero. On a protractor, it reads 90. So it's an unending source of confusion for people. RON HAZELTON: So Mark, show me how it works.
A ruler is used to measure units of length, inches, feet and yards. Standard rulers have inches on one side and centimeters on the other. A typical ruler measures up to 12 inches, and is equivalent to 30.48 centimeters. This is also equivalent to 1 foot. Each inch on a ruler has markings in between that are a fraction of an inch.
Get a metric ruler. A metric ruler uses the metric system, which measures in centimeters instead of inches. There should be 30 centimeters on the ruler, which are designated by large numbers on the ruler. Between each centimeter (cm) mark, there should be 10 smaller marks called millimeters (mm).