The first letters of the most popular prefixes in the metric system can be remembered by memorizing the phrase "King Henry doesn't usually drink chocolate milk." The first letter in each word of the phrase corresponds in descending order with the first letters of prefixes kilo, hecto, deca, unit, deci, centi and milli.
The metric system is the most widely used system of measurement in the world. It was first introduced in France in 1799, and has since become the official measurement system in every country around the world except for the United States, Liberia, and Burma. The system uses a single unit of measurement, such as grams or meters, and uses prefixes to describe that measurement in factors of ten. For example, a kilometer is 1,000 meters, and a kilogram is 1,000 grams.
The metric system allows for easy conversion between units of measurement, and even measurement types. In the imperial system, there is no base conversion for heat, mass, length, and volume, but in the metric system a single unit of each measurement corresponds to a single unit of another type of measurement. For example, 1 calorie is the amount of energy it takes to heat 1 gram of water 1 degree Celsius. Also, all subdivisions of measurements are based off of the number ten, making conversions very easy.