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.
Lets try a example, I measure my desk, I get my rule and hook one end and pull it to the other end. It will show on my rule 47 3/4 inches, it will read 47 3/4 inches on one side and the other side will read 3 foot 11 3/4 inches , ( see illustration above to find the 3/4 mark on the rule). Try measuring things around the house and you will see how easy it can be to read and understand measurement.