The metric system was created in France in the 18th century, and is based on a decimal system. Each base unit, such as a meter, the unit of length, can be broken into pieces or multiples based on powers of ten. Most countries in the world have adopted this system.
The meter stick is the most common metric ruler. It measures one meter in length, or the equivalent of just over 39 inches. The meter is the basic unit of measurement of length in the metric system.
The meter stick is broken into 100 equal subdivisions called centimeters. There are approximately two and a half centimeters in an inch. The meter stick usually marks off every ten centimeters in a larger or darker font.
Each centimeter is then divided into 10 smaller pieces called millimeters. A millimeter is one one-thousandth of a meter. Your metric ruler typically has hash marks between the centimeters that represent the millimeters.
In order to read the metric ruler, you do not have to use fractions like on a ruler that has inches. When measuring, merely use the decimal system, indicating 89 centimeters and 5 millimeters as 89.5 cm, for example.