## Decimal Metric System

Since ancient times, people have been creating their units of measurement. Each had its own standard units. With the development of trade, it became increasingly difficult to exchange information and negotiate with so many different measures.

It was necessary to adopt a unique measurement standard for each quantity. Thus, in 1791, the time of the French revolution, a group of representatives from various countries met to discuss the adoption of a single system of measures. The decimal metric system appeared.

## Subway

The word metro comes from gegro *metron* and means "what measures". It was initially established that the meter would be the tenth millionth of the distance from the North Pole to Ecuador on the meridian passing through Paris. In Brazil, the metro was officially adopted in 1928.

## Multiples and submultiples of the meter

In addition to the fundamental unit of length, the meter, there are also their multiples and submultiples, whose names are formed using the prefixes: kilo, hecto, deca, deci, centi and milli. Look at the box:

Multiples | unity | Submultiples | ||||

kilometer | hectometer | decameter | subway | decimeter | centimeter | millimeter |

km | hm | dam | m | dm | cm | mm |

1,000m | 100m | 10m | 1m | 0.1m | 0.01m | 0.001m |

Multiples | kilometer | km | 1,000m |

hectometer | hm | 100m | |

decameter | dam | 10m | |

Core Unit | subway | m | 1m |

Submultiples | decimeter | dm | 0.1m |

centimeter | cm | 0.01m | |

millimeter | mm | 0.001m |

Multiples of the meter are used to measure large distances, while submultiples for small distances. For millimeter measurements where accuracy is required we use:

micron (µ) = 10^{-6} m

angströn (Å) = 10^{-10} m

For astronomical distances we use the Light Year (distance traveled by light in one year):

Light year = 9.5 · 10^{12} km

Foot, inch, mile, and yard are non-decimal metric units being used in English-speaking countries. Note the following equality:

Foot | = | 30.48 cm |

Inch | = | 2.54 cm |

Yard | = | 91.44 cm |

Land mile | = | 1,609 m |

Mile | = | 1,852 m |

Notice that:

1 foot = 12 inches

1 yard = 3 feet

Next: Reading Length Measurements