In the United States the Imperial System of measurement is commonly used, but most of the world uses the metric system. Graphics, diagrams and video teach us about the history of the metric system, base 10 system, measuring distance, prefixes used with the word meter, measuring volume, liters and milliliters, measuring mass, the difference between mass and weight, grams, kilograms, metric tons, and milligrams. The metric system is very easy to use. Multiple-choice reviews at the end of each segment reinforce important concepts.