International System of Units
The International System of Units standardizes the units of different quantities to facilitate their use around the world.
The International System defines a group of seven independent quantities called base quantities . From them, the other quantities are defined and have their measurement units established. These quantities defined from the basic ones are called derived quantities . The tables below bring the two types of magnitude, as well as their measurement units.
There are some quantities that do not have units of measurement, as they are the result of the division between two equal quantities. This is the case of the refractive index , which is defined from the ratio between two velocities. This type of quantity is called a dimensionless quantity .
In specific fields, such as commerce, health, education, industry, etc., each country can establish its own rules for the use of measurement units for quantities. In 1955, the International Organization of Legal Metrology (OIML) was created, which takes care of the international harmonization of the legislation of the countries in relation to the units of measurement.