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The acronymn "King Henry Does Usually Drink Chocolate Milk" is used to teach the metric system. The first letters of the words represent kilo, hector, deka, unit, deci, centi, and milli.

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**King**
**Notation**
The **International System of Units** (abbreviated **SI** from French: *Le Système international d'unités*) is the modern form of the metric system and is the world's most widely used system of measurement, used in both everyday commerce and science. It comprises a coherent system of units of measurement built around seven base units, 22 named and an indeterminate number of unnamed coherent derived units, and a set of prefixes that act as decimal-based multipliers.

The standards, published in 1960 as the result of an initiative started in 1948, are based on the metre–kilogram–second (MKS) system, rather than the centimetre–gram–second (CGS) system, which, in turn, had several variants. The SI has been declared to be an evolving system; thus prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses, and as the precision of measurements improves.

The **International System of Units** (abbreviated **SI** from French: *Le Système international d'unités*) is the modern form of the metric system and is the world's most widely used system of measurement, used in both everyday commerce and science. It comprises a coherent system of units of measurement built around seven base units, 22 named and an indeterminate number of unnamed coherent derived units, and a set of prefixes that act as decimal-based multipliers.

The standards, published in 1960 as the result of an initiative started in 1948, are based on the metre–kilogram–second (MKS) system, rather than the centimetre–gram–second (CGS) system, which, in turn, had several variants. The SI has been declared to be an evolving system; thus prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses, and as the precision of measurements improves.

**Centi-**
**Chocolate**
**Deci-**
The **metric system** is an internationally agreed decimal system of measurement that was originally based on the *mètre des Archives* and the *kilogramme des Archives* introduced by France in 1799. Over the years, the definitions of the metre and kilogram have been refined and the metric system has been extended to incorporate many more units. Although a number of variants of the metric system emerged in the late nineteenth and early twentieth centuries, the term is now often used as a synonym for "SI" or the "International System of Units"—the official system of measurement in almost every country in the world.

The metric system has been officially sanctioned for use in the United States since 1866, but it remains the only industrialised country that has not adopted the metric system as its official system of measurement. Many sources also cite Liberia and Burma as the only other countries not to have done so. Although the United Kingdom uses the metric system for most official purposes, the use of the imperial system of measure, particularly in unregulated sectors such as journalism, is widespread.

**Litre**
**Milk**
A **system of measurement** is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce. In modern systems of measurement, some quantities are designated as fundamental units, meaning *all other needed units can be derived from them*, whereas in the early and most historic eras, the units were given by fiat (see statutory law) by the ruling entities and were not necessarily well inter-related or self-consistent.

**Measurement**

A **metric prefix** or **SI prefix** is a unit prefix that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol. The prefix *kilo-*, for example, may be added to *gram* to indicate **multiplication** by one thousand; one kilogram is equal to one thousand grams. The prefix *centi-*, likewise, may be added to *metre* to indicate **division** by one hundred; one centimetre is equal to one hundredth of a metre.

Decimal multiplicative prefixes have been a feature of all forms of the metric system with many dating back to the system's introduction in the 1790s. Metric prefixes have even been pre-pended to non-metric units. Today the prefixes are standardized for use in the International System of Units (SI) by the International Bureau of Weights and Measures in resolutions dating from 1960 to 1991.