When buying a dial indicator, for example, and you choose one that has millimeter graduation instead of inch graduation, that means you choose the metric dial indicator. The term metric dial indicator means the dial indicator that uses a metric unit system.

Dial indicator is not the only measuring tool that uses metric or imperial or both. There are so many instruments that use these two systems.

Learning the metric unit system can be important. If you live in the countries where the imperial system is commonly used, learning this system lets you know what metric unit to use for someone in the countries that use metrics. For example, to express length, you use kg instead of pound for someone in Japan.

The metric system is also officially used as the international reading system. And there are other benefits of learning this system.

## So, What is Metric Unit System?

A metric unit system is the unit system that uses meter, gram, second, ampere, kelvin, candela, and mol as the base units. These units are actually originated from the 7 fundamental physical quantities. Then this system has derived units to express other further physical quantities (the other quantities that are derived from those 7 fundamental quantities). Aside from that, it has some prefixes to express the unit magnitude.

The purpose of the metric system is to unify dozens of the previous measurement systems.

Since it has a good naming structure, the metric unit system is usually used for scientific and technical purposes. Under the monitoring of the International standard body, then the metric system becomes the International System of Units.

## The Background of Metric Unit System

It is stated that before the development of the metric system in the 18^{th} century, there were many measurement units used in the world [Source: Anthony Carpi, Ph.D.].

For instance, we measure the length in the units of inches, spans, hands, palms, miles, feet, rods, chains, etc. Inches, miles, and feet can be found in the imperial unit system.

These different measurement units for one quantity brought confusion. Therefore, the French government aimed to develop a standardized measurement that can be used worldwide.

In 1790, the decimal-based system of units was made. Then, in 1960, the metric system officially turned to SI. It is the abbreviation for the International System of Units.

The metric system is made based on the natural physical unit when French Revolution occurred. The establishment was proceeded by the National Assembly leading the French Academy of Science to tackle the confusion due to the great number of traditional measurements.

As the metric system was created, it solves the chaotic condition led by dozens of measurement systems that needed to be unified. In this case, the International System of Units begins to unify many measurement systems.

## The 7 Major Metric Base Units

There are 7 fundamental physical quantities that are measurable: length, mass, time, electric current, temperature, luminous intensity, and amount of substance. The reading units of these fundamental quantities are called the base units. Since it’s in a metric system, it becomes metric base units.

For further details, the base quantities and base units will be shown in the table below:

Base Quantities | Base Units | Symbol |
---|---|---|

Mass | gram | g |

Length | meter | m |

Time | second | s |

Electric current | ampere | A |

Temperature | kelvin | K |

Luminous intensity | candel | cd |

Amount of substance | mole | mol |

## Metric Prefix System

In the metric system, you can use prefixes such as exa-, kilo-, hecto-, deca-, milli-, centi-, and many other prefixes.

Sometimes, when you have to express 1.000.000.000.000.000.000 gram, it can be very time-and-space consuming to write down. Herewith, you could use one of the prefixes officially available. Simply add the “exa-” prefix before the gram. Now, it becomes 1 exagram. Every time you read 1 exagram, you know it is 1.000.000.000.000.000.000 gram.

These prefixes can be seen in the table below.

Prefix | Factor by which base unit is multiplied | Symbol |
---|---|---|

exa- | 10^{18} = 1.000.000.000.000.000.000 | E |

peta- | 10^{15}= 1.000.000.000.000.000 | P |

tera- | 10^{12}= 1.000.000.000.000 | T |

giga- | 10^{9}= 1.000.000.000 | G |

mega- | 10^{6}= 1.000.000 | M |

kilo- | 10^{3}= 1.000 | k |

hecto- | 10^{2}= | h |

deca- | 10 | da |

base unit | 1 | |

deci- | 10^{-1}= 0.1 | d |

centi- | 10^{-2}= 0.01 | c |

milli- | 10^{-3}= 0.001 | m |

micro- | 10^{-6}= 0.000001 | μ |

nano- | 10^{-9}= 0.000000001 | n |

pico- | 10^{-12}= 0.000000000001 | p |

femto- | 10^{-15}= 0.000000000000001 | f |

atto- | 10^{-18}= 0.000000000000000001 | a |

## Derived Units of Metric System

If a certain unit comes from two or more base units, it is a derived unit. For example, a speed (meter per second) is derived from length (meter) and time (second); from the mathematical combination of the metric base units

That being said, derived units are the units that are generated from the base units. Since it uses metric base units, the derived units are said metric derived units.

There are many derived units; the table below will portray some derived units in the metric system.

Quantities | Derived Units | Symbol |
---|---|---|

Area | Square meter | m^{2} |

Volume | Cubic meter | m^{3} |

Speed, Velocity | Meter per second | m/s |

Accelaration | Meter per second squared | m/s^{2} |

Wavenumber | Reciprocal meter | m^{-1} |

Mass density | Kilogram per cubic meter | kg/m^{3} |

Specific volume | Cubic meter per kilogram | m^{3}/kg |

Current density | Ampere per square meter | A/m^{2} |

Magnet field strength | Ampere per meter | A/m |

Amount of substance concentration | Mole per cubic meter | mol/m^{3} |

Luminance | Candela per square meter | cd/m^{3} |

Mass fraction | Kilogram per kilogram | kg/kg |

In addition to derived units, there are derived units with special names. You can see some details of derived units with special names in the table below.

Quantities | Derived Units | Special Names | Symbol |
---|---|---|---|

Plane angle | m. m^{-1} = 1 | Radian | rad |

Solid angle | m^{2}. m^{-2} = 1 | Steradian | sr |

Frequency | s^{-1} | Hertz | Hz |

Force | m.kg. s^{-2} ^{2} | Newton | N |

Pressure | m^{-1}.kg. s^{-2} | Pascal | Pa |

Energy, Quantity of heat | m^{2}.kg. s^{-2} | Joule | J |

Power Radiant flux | m^{2}.kg. s^{-3} | Watt | W |

Electric charge, Quantity of electricity | s.A | Coulomb | C |

Electric potential difference | m^{2}.kg. s^{-3}.A^{-1} | Volt | V |

Capacitance | m^{-2}.kg^{-1}. s^{4}.A^{2} | Farad | F |

Electric resistance | m^{2}.kg. s^{-3}.A^{-2} | Ohm | Ω |

Electric conductance | m^{-2}.kg^{-1}. s^{3}.A^{2} | Siemens | S |

Magnetic flux | m^{2}. kg. s^{-2}. A^{-1} | Weber | Wb |

Magnetic flux density | kg. s^{-2}.A^{-1} | Tesla | T |

Inductance | m^{2}.kg. s^{-2}.A^{-2} | Henry | H |

Luminous flux | m^{2}. m^{-2}.cd= cd | Lumen | lm |

Illuminance | m^{2}. m^{-4}.cd= m^{-2}.cd | lux | lx |

Activity of radionuclide | s^{-1} | Becquerel | Bq |

Absorbed dose, specific energy | m^{2}. s^{-2} | Gray | Gy |

Dose rate | m^{2}. s^{-2} | Sievert | Sv |

Catalyc activity | s^{-1}.mol | Katal | kat |

There are also some non-SI unit names but we can use them with SI such as liter (volume), minute (time), hour (time), etc. The conversion from liter to cubic centimeter is 1 to 1000.

## What Countries Do Use the Metric System?

Almost all the countries use the metric system except these 3 countries: the United States, Myanmar, and Liberia. Those 3 countries have to use the metric system to connect with other countries.